A dedicated room inside the shop with things sized and priced for younger visitors.
Kids tend to be good at this. They pick things up, ask what it is, want to know where it came from. The kids gallery is stocked with that in mind: things that are interesting to hold, priced so buying one isn't a big deal.
[Add a few specifics about the kids gallery: what kinds of things are in there, rough price range, anything that makes it stand out. A sentence or two is plenty.]
If you're at Table Rock Lake with kids and looking for something off the water, it's worth stopping in. A crystal or a fossil makes a better souvenir than most of what's sold around the lake.