He calls us to preach His Word and live His life and share His Good News. Size is His department, not ours. We can learn and grow and be challenged by anyone whether they are a child, or a young person, or a someone really, really old. I sometimes think that I learn more from my children than they do from me. Still there is a truth here.
Faith is faith whether young or old and it is the engine that runs the Kingdom.
What we do by faith, and not in our own efforts is what really builds His Church. It is our natural tendency to stop acting in faith and start working in and trusting in our own efforts and abilities. David had a children's moment ready. Maybe, as I said before, he would have had that time in the service even if we weren't there and their wasn't a squirming kid for as far as the eye could see. I don't know.