What can i do with a three year old boy while babysitting?

When he comes over we go swimming and i play this game with him where we go on a treasure hunt and he gets to take something home with him. When he comes over his 8 year old brother comes too. Does anybody know anything that we could do because sometimes we get bored and im like ummmm what do u guys want to do? games or print outs would be great. any ideas? keep in mind that the three year old cant play bored games and he is not good at the computer. the eitght year old loves the computer and doesnt like bored games. thanks! and by the way they are both boys i cant remember if i said that already lol