The kids will be fine in the cheap ones. Spend a little more on your comfort if you have to so you can enjoy family time.
J & H Lanmark Outdoors store in Lexington is having a kayak demo this Saturday at Jacobson Park on Richmond Rd. Check out their website or give them a call. You can demo all the kayaks they have and get a lot of good info at the same time. Be prepared to get wet and have a good time.