This Advent when we light our Advent wreath we are saying this simple prayer from
Faith and Life 1. We used it for a few years when my older girls were small:
Thank you, dear Jesus,
for coming down from Heaven to save us.
Thank you for Christmas time.
Help us to get ready for your coming this year.
Amen
Here I found another prayer suitable for younger children:
O God,
as light comes from this candle,
may the blessing of Jesus Christ come to us,
warming our hearts and
brightening our way.
May Christ our Savior bring life
into the darkness of this world,
and to us, as we wait for his coming.