Help with wooden crafts?

I bought 2 little unfinished wood treasure boxes, some paint and some stickers. My 9 yr old nephew loves Ohio State Football so one of them Im sponge painting red and using gray letter stickers to put Ohio State on it and his name. I also bought little football stickers to put on it. The 6 yr old nephew is into Moster Trucks, Harley's, Semi Trucks, anything powerful with wheels and a motor and he likes John Deere. so I am sponge painting his John Deere Greeen and his name in stickers. My question is, what can I put on his as a lable? Im putting Ohio State Football on the other one. Also, I have never sponge painted, any tips? Should I buy that stuff to make them look "crackeled" and should I varnish or polyurethane them to make them shiny and keep the stickers from coming off. I have an 18 month old niece, think she she is too young for something like this? I mean the boys can put little treasures in them but what can an 18 month old do with one except put it up and later in life say her Aunt hand made it for her? BTW, these are Christmas gifts. Im going to put candy or football/monster truck cards or something in them. If you have other ideas of what to put in them, by all means I appreciate all suggestions. thanks!

Help with wooden crafts?