The easy thing about the computer is it doesn’t require your constant interaction with them. It may be hard for you to get busy playing with them when you have to make supper and also just walked in the door, etc. One thing that is much better is tapes (today it’s cd’s) appropriate for their age. Jewish tapes are very educational and enjoyable for them – not on the computer – then the imagination is being used while listening.
Midos Machine, Mitzvah Tree, Rabbi Juravel on the Parsha, and they absolutely love Morah Music and will dance and sing and act out everything, esp. once you teach them what’s going on in each song. (I think more than one may have come out, we only have the first one.)
Also, soon the weather will be warm and they can play outdoors. You didn’t say if they are boys or girls, but I have a 4 year old girl who loves doll carriages – I buy them in the Flea Market for a few dollars – she has a few of them and constantly cares for her dolls. Any new toy for a child will draw them off the computer, large puzzles, and then you can make the computer off limits until a later hour (if there are older children who will turn it on anyway.)