My kids are 4 and 7 and both of them love to play with lego but they also like TV cycling and CBBC web sites. I think the important thing is that they have a good balance between all forms of play.
I think that as a lego fan myself it gives my children an I some common ground where we can play together they like to play with my creations and they ask for help with their creations This builds a good bond between parent and child which is something a lot of kids who are just stuck infront of a games console sadley do not have.
Computers and TV are a huge part of todays life but as a parent you need to take a resonsible attitude to what they can have access to.