World of Zoo is fun and cute, especially if they like animals.
(Plus, it's not too pricey either.)
It's definitely a game geared toward younger children, and you can't really lose. I couldn't say how long it'd hold their attentions for... but if they like animals, it'll probably keep them captivated for a while. (The PC version is only $5 too, so it could even make for a nice stoking stuffer.)
SimAnimals, which is really similar, is around the same price. Of the two, I think a 4 and 5 year old would have a better time with World of Zoo.
Almost any of the MySims games are great (but stay away from MySims Racing and MySims Party). Like World of Zoo, you can't lose, and it's fun, cute, and a game I feel they'd enjoy for a while. (Out of all the MySims games, I recommend Kingdom the most.)
Check out some youtube videos of both games to see what you think they'd like more
I don't think either of those games are multiplayer though, but I think your kids would enjoy them.