Raising Kanes,

Since you wanted to make it more formal and traditional, why use those four themes?

(I'm reminded of an assignment I gave students eons ago, to which one student came unprepared. The students were to prepare a 'picture description' in French. She asked permission to go the computer lab to get a picture, typed in "French girls" and was about to press "enter" when I intervened, worried about what such a search string would bring up.)

I recommend the following, which will make your search easier:

Prophecy (John the Baptist or OT prophets)
Mary
Nativity
Adoration

For what it's worth, I would also steer light-years away from anything that calls itself "children's choir piece" Most of the publishers and composers think "children" means "infantile".

If you're looking for suggestions for pieces, try the Huron Carol, I Saw Three Ships, Of One that is So Fair and Bright, Of the Father's Love Begotten. If you can get away with Latin, use the Magnificat Antiphons from the 17th to 23rd, and follow up with O Come, O Come Emmanuel.

This fits the four themes at least . . .
this too
and this
and this
this
and even this

Just hinting that the "theme" is a well-worn one in certain circles.