Well you can always send them over here. Then when they go outside your youngest can let me cat out again and they can all help me hunt her down in the trees out back.
I've seen that your kids as well as my daughter are addicted to TV. When there's other kids around as sometimes is the case here they will stay outside much longer. In fact last time they were here your eldest was outside for about 2 or 3 hours (can't exactly remember but it was at least 2 hours) and the others were in and out a lot.
Sometimes I'll turn on CMT on the TV. Gives me music and "occupies" the TV. My daughter doesn't bug me to use it then. I find if I go out with my daughter she'll stay out longer. If I'm inside on the computer or just putsing around the house she'll inevitably migrate to the computer or television.
Then there's the sandbox. That works wonders for my daughter. When I had a small sandbox here she was ALWAY in that thing. Rain or shine practically. I'm sure your youngest would find it just as facinating as they seem to share similar interests.
When I put up the simple swing here my daughter gravitated toward outside even when she was completely alone out there. It was almost a chore to keep her inside in the morning just so I could shower without her wandering away.
In the end it will be a constant battle I think. I sometimes find myself drawn to the TV and especially the computer instead of doing what I should around the house, going out and getting excercise, or being productive in some way.