Warioware is a very fast paced game which may set some kids off but all of the mini games are simple. My son's 4 and 6 have played very little of warioware but they do use it more than monkeyball. Regarding Monkeyball its kind of hard to say ithe 1 player adventure mode difficulty may jump beyond a 4 year old's ability after the first several stages. There is alot of minigames that a 4 year old would like though but unfortunately alot of them have control issues. If your son can handle the fast pace I would recommend Warioware.