Ideas of things to do

I have 3 kids ranging from 4 - 12 and I've often found it difficult to find something that we can all do together without any complaints. What is usally great for the 4 yr old is boring to the 12 yr old! And whats fab for the 12 yr old is too advanced for the 4 yr old. I have recently had my fair share of grief this month and want to do something to show my kids I love them, some special time and I'm just so stumped, any ideas would be greatly appreciated. Many thanks in advance x