My youngsters are a little older than yours but we've been going there since they were dinky (DS was 2 went we first took him). There are enough of smaller rides to fill a day (bubbleworks, tiny truckers, carousal, jungle bus, tombraider, flying jumbos, bouncing berrys, tuks turmoil safari skyway ) and to fill in any gaps theres the play areas in the Dragon area and the new Madagascar Live show (if you can stand it personally I like the old much smaller dragon puppet show better)
It's also quite good for kids that want something a little more exciting too. if yours are slightly adventurous they'll probably enjoy the runaway mine train, both mine also enjoyed the vampire ride at 4, but they are quite tall and like faster rides (vampire has no upsides downs). DD liked Hocus pocus hall at 3, but DS is absolutely petrified of the thing!!!
The zoo I think makes a big difference too, and to be honest it's one of the reasons we prefer Chessington to Legoland. Its nice to take time out in the middle of the day and there are lots of animals shows. So far we've only caught the sealion and the one in front of the manor. but DC really enjoyed them.
Hmm looking at the above I think I should be on commission
Terms and conditions: Lead price based on two adults and two children sharing a room at the Holiday Inn Woking on Fridays and Sundays. Onsite lead price based on a family of four staying at the Chessington Resort Hotel on selected dates during term time. Offer ends 28 February 2013. Subject to change and availability.