We have a strict rule in our house that no television until the homework is done. After that, my daughter is allowed an hour of television. She's not really into computer games etc, so that has never been an issue. She is quite active outside of school and has joined many clubs - singing club on Mondays, cheer leading on Wednesdays, youth club on Fridays, roller skating on Saturdays. Luckily she loves the outdoors and would rather be out playing with her friends or in the garden. She uses her laptop around an hour a day, and keeps in touch with her friends on the cell phone, but not excessively.
I think it is all about encouraging our children to become more active and take part in out of school activities. We quite often go for a walk, or visit the library. Children need to be stimulated and encouraging them in an activity that they enjoy may help them steer away from tv and computer. Doing some crafts together is an enjoyable distraction from technology. My brother and his son go to football matches together and make bird boxes as a hobby. Teaching them new skills and encouraging them to try other hobbies will give them variation too.