Ben 10 has a special watch and chases away all kinds of scary monsters with his special watch ... or something like that. If you're thinking about presents to do with Ben 10, then Woolies would be your best bet.
Nooo greenday - it looks like a watch but it is an omnitrix which means he can use it to turn into whatever alien would best suit the situation. He has 10 to choose from including greymatter (the smart but weedy one), Four arms (big strong guy with er 4 arms) and Stinkfly (you can guess)etc, etc.
I have had many conversations with my DS1 about it