First:

Welcome to the Forum.

With children, reinforcement is the key. They will sing well what they've come to internalize.

Start small: depending on the abilities of the group, you may have to start with a group of soloists doing most of the work, and the larger group singing only one piece of music.

Whatever you do, don't cater to the parental attitude (found in adults who aren't parents, too) that age appropriate means childish when it comes to music.

Kids that age are sponges. Expand your time with them by finding a way to play music at lunch, and before long they'll be humming whatever it is you've been playing.

Jackson beat me to it: teach them basic breathing and matching pitch exercises.

Expect more grown up behaviors, and you will get them. Expect childishness, and this is what you'll get.

Chant being pure melody, it will be a natural for them all to learn to sing (and pronounce) together.
when they're ready for part singing, simple canons can be a way to introduce it

To me, the wondrous thing about children's choirs is the ability to learn. Those bare little hard drives just pick things up faster than I can believe. Have fun ! Let us know how it goes!

Jen,

I think the first place is to start with unison. It will give you an opportunity to observe a) musicality that is available within the group and b) gauge interest on particular pieces. In other words, as you discover that a sizable portion of the group are interested in a particular piece - a "favorite" for the group - that gives you something to come back to with 2-part. I agree with MJO above that 4-part is likely not in play for this age-range... but the way to 4-part is to start with 2 (and eventually) 3 part. When you are ready for going to part music, a lot of pieces lend themselves to the top two parts... especially if you have the organ providing any additional parts underneath.

Don't be afraid to sing-along (practice and Mass)... or if you have an assistant, for both of you to sing along. There is an advantage to having an example to follow (particularly when you get to parts), just as there will be an advantage to stopping to sing when they reach a comfort-level with doing it on their own.

Since you home-school, you may already be familiar with a key piece of the puzzle... namely, the preparation that YOU do in advance. Just as you would have lesson plans for teaching curricula through the year, you'll need to think through the entire year in advance. The good news is that it sounds like you are talking 12 Masses at most. The bad news is that 50 min. per week is not necessarily a lot of time, particularly with 30-50 children.

Let's say you start in September. Build a music schedule September through ... ?? (the end of the year for the children) of the hymns, chants, and responsorials you will sing. Are you singing the parts of the Mass as well (Kyrie, Gloria, etc.)? Will you need to prepare responses? An ideal music schedule will allow for SOME duplication of effort and SOME growth. (Maintenance and building for the future.)

Then build a practice schedule that fits the weeks you have to practice in advance of each month against the pieces that need to be rehearsed. You likely won't have 50 minutes each week - some of it may be administrative time (roll-call?). Will there be weeks you'll lose time because of other school-wide things (school play, poetry recital, etc.)? Are you going to have to spend part of your time with Latin pronunciation (for example), or explaining some basic music theory? (Probably).

In the end, divide your practice plan into segments. Maybe 3-4 segments per practice session (15 minutes / 15 minutes / 10 minutes / 10 minutes) understanding that "15 minutes" may only be 10 if you have roll-call, for example. Assign your items into these blocks. A single piece may take 2-3 blocks, or it may be a single block of time.

If you do this for the entire year in advance, you may find - after writing your practice schedule - that you have to tweak the music schedule a bit. After a bit of back-and-forth between the schedules, you'll have an overall plan that you'll feel reasonably comfortable with - at the beginning of the year.

Once you start practices, revisit your plans each week. Are things going as smoothly as you hoped? Are you encountering challenges you didn't expect? Adjust the plans for future months as needed to account (either because of bumps in the road or to accelerate time-lines because the children are eating it up).

You want the experience to be rewarding - both spiritually and (truth be told) emotionally for the children. There's no reason to suspect - given your post - that it won't be both! Kudos for taking it on - and prayers for your success!!

Pueri Cantores has a list of recommended repertoire, including unison and two-part works, at
https://www.pcchoirs.org/repertoire-suggestions-young-catholic-choirs

One point I would like to add. I have noticed that many children who have sung in children's choirs that have focused on "kiddy" sounding music will eventually grow up not knowing any of the music that is sung at the "regular" parish masses. I believe children should learn at least some of the traditional repertoire that any adult Catholic should know. Include some common traditional hymns for each season and some chant (Latin and/or English). You could even teach them some of the simple ICEL chant responses such as the Preface Dialog or Dismissal. Teach them the same mass setting(s) generally used at parish liturgies. They should feel that when they are not singing in the choir (or when they age out of it), they can still fully participate in the singing at any parish mass.

I use about 15 minutes each lesson to teach Ward method and then work on the music for the upcoming Mass for the month and also to increase general repertory. I typically split the group at the halfway point, dismissing the younger children and working on more difficult repertory with the older ones. They do like singing rounds... there is a GIA publication by William Tortolano that is very nice -- 59 Liturgical Rounds.

I do use some silly songs with body motions to keep the attention of the youngest ones (my youngest is 3 years old) and find that the older kids like them, too. They all like two songs I learned from Wilko Brouwers -- Djingala dja and Welcome to my Forge.

More suggestions. Utilize responsible parents as volunteers to help with organizing. Perhaps they could file music, prepare folders, assist in vesting singers if vestments are used, create car pools, organize choir outings or simple refreshments afterwards, chaperone field trips (such as visits to hear other choirs or sing with festival groups), and (choose carefully and discretely) help supervise singers in rehearsal, escort them to restrooms or water fountains, and help monitor dismissals and child-pick up. About dismissal and pick-up, you have to be very firm about expectations that children are "claimed" with-in fifteen minutes of conclusion of rehearsal.

Hi Jen.
Not sure if this is still relevant but I’d like to add my two cents. Every year I get a new group of 40-50 4th graders and I prepare them for weekly school masses, the monthly Sunday school mass, and occasional participation in a choir festival.
Some years I have very cooperative classes, some years I have to ask some students to sit with the other grades in the pews. On Tuesdays I rehearse with them for 30 minutes. Then warmups and mass on Thursday mornings. Here are some techniques I use that seem to be working.
Rhythmic breathing for time
Siren wailing (highest to lowest notes)
Solfege games with hand signs
Hymn study
2 part hymn arrangements
Chant study
Latin study
Conducting lessons
Schola/choir alternation
Cantor opportunities
Choral techniques (vocal/postural)
Basic reading

All these things can be incorporated. But the exact “how to” needs to be tailored to your situation.

Some advice. When you have less than an hour of instruction per week to work with, you have to make every minute count. Talk little, do a lot. Don’t plan to do more than you can actually rehearse well. And don’t hide behind the piano, plow through music and assume that most will get it right. If you can’t find ways to make disruptive kids productive, ask them to participate in something besides choir. Never let them forget: glorification of God and edification of the faithful, what an awesome responsibility!
Wow, sorry for the rant! My choir doesn’t sound exactly like fun, but the kids do end up singing some chants and hymns for fun when I’m not engaging them.
You have my prayers!