In my new parish (now there almost two years) we don't have a school and thus school Masses. This academic year I decided to have a more "child-friendly" Sunday Mass once a month.
While it is child friendly, it is not childish.
We have a wonderful children's choir and a child cantor who is as good as any adult I have heard, in fact her voice has an adult sounding quality. She can sing complicated music.
We have children lectors and greeters.
At the homily time I invite the children to the sanctuary and preach to them but something that isn't childish but on their level (and the adults say they get more out of my children's homilies than my normal ones, but I digress).
But the children's Mass isn't childish. It is digified and I believe prepares these children to become adult Catholic worshippers. There are no gimmicks or cute things that we do or anything that is unusual in terms of errant creativity.
Yesterday we celebrated our second graders' First Holy Communion. It was splendid and in every way like a normal Sunday Mass with all the bells and smells (incense) possible.
The children came in single file to the sanactuary to receive their First Holy Communion, individually receiving Holy Communion while kneeling. They received Holy Communion under both forms by way of intinction. I held the ciborium while the deacon held the chalice and each child was instructed how to receive properly on the tongue. (They know, too, how to receive in the hand properly according to our unfortunate norms.)
The Mass and children were completely reverent and devotional as though it was an Extraordinary Form Mass which it wasn't.