Frankly, I haven’t yet discovered a way to compete with churches that have all the buzzers and whistles with full-blown kits and activity sheets for kids. But that’s certainly not reproducible. The next small group you reach into may not have that money to fund the “wow.”
I have learned from house churches to tell the story, review the content, and then separate the really young children for a special age-group activity (coloring or making a craft usually) while the parents discuss the story in depth. Afterwards, the kids return and do a show-and-tell.
Often teens serve as facilitators for a group not their own to help out. And college kids are “paid” by being allowed to do laundry while they’re helping. A home-cooked meal is a good incentive, too.
The Bible studies that I do are developed with kids in mind. I try to pick stories that aren’t too gruesome, for example, (think Jephtha’s Daughter in Judges) and yet keep adults engaged. I mean, Noah and the Ark is a great story, but there’s lots of death that is glossed over.