Start with the smaller rides and see how everyone responds - they will see the bigger attractions such as Splash and Big Thunder Mountain and they may beg you to go on them or maybe one or both will feel uncomfortable about them.
(You can have two together on Big Thunder).
Splash has so much going on before the big drop, it is a great shame to miss this out, (and as Hilary says, you can sit next to each other on this too), but you can watch the 'logs' coming down from the bridge and anyone who finds it really daunting should perhaps leave it out.
You can also catch a glimpse of the inside of Space Mountain by riding the Tomorrowland Transit Authority. Space is the only ride in MK where you sit one behind the other (has a minimum height of 44").
There is no need for you all to miss out - you can use the parent/guardian switch (aka baby swap) if both parents want to ride and one or both children don't or can't - approach the Cast Member at the ride entrance and they will advise you as this is different for different attractions, but basically it means you won't have to line up for a ride twice.
Definitely start with Disney before Universal's IOA park - the rides are bigger in IOA.
The older Universal park attractions are more film experiences rather than heavy rides - except for Back To The Future which is a wild simulator!
It is difficult to cover all the attractions in one post and all the different types of thrill ride but I'd suggest firing more questions at us - we love talking about rides
!! - and perhaps reading up about the rides.
We have info on these at
www.wdwinfo.com
Tell us more! Where are you staying and how long are you there for?
but only you know what your kids would and wouldn't like
