This would be an excellent Moment for a Music Sunday.
Ideally, you will know, by name, all the children who are in church that day. If not, use groups like “First Graders” or “Girl Scout” and finally “All the Little Children.” When it is is time for the Moment, begin by singing “HE’S GOT THE WHOLE WORLD IN HIS HANDS.” After the first course, continue, using the Children’s names (“He’s got Adam and Betsy, in his hands, He’s got Carol and David, in his hands…”) As you sing each child’s name, go to them or motion to them to join you. (It may be best to cue some of the older children as you call them, so the younger ones will follow.)
Once all the Children are together, tell them that prayers come in many different forms, from quiet words, to silent thoughts and happy songs. And that “each one of you can pray in your own special way and God will hear your prayers – because each one of you is a Child of God.”