Whilst little toys and figures are quite sweet for the kids I'm getting a bit bored with them. They're in almost every cache that I visit.
I'd recommend something a little more interesting/practical for 'bigger' kids what about a small book of stamps (in a little plastic bag in case the cache is a bit damp), or some funky little bits of stationery or little sewing kits... something a bit more interesting and a pleasure to find. Its a positive feedback thing... the better the stuff you leave the better the quality of the caches and so on and so forth. Of course this works in reverse too as I am increasingly finding.