Why not sign up for a fitness session with your kids?
I have a few clients that bring in their child when they come visit me. For the first 30 mins, I work out with mom. Then mom gets on the treadmill and I work out the child. It works out great! Both get a great workout, at it provides them with a great opportunity to bond together.
There are many different classes you can take together. Check your local gym to see what kind of classes they offer and check them out, together!