Edinburgh with kids and Grandparents?

My parents want to spend some time with us in 2011 without actually setting foot in our house (long story, don't ask!).  Mom wants to be able to fly directly or really close to wherever we go but otherwise says it's up to us.  I checked and they can fly Delta from Atlanta to Edinburgh.

Is it a good place to visit for a preschooler?  We're talking mid april to mid may time of year.

Any recommendations of cottages/apartments to rent that will sleep five?

IMHO Scotland is a very kid friendly place. And everywhere is so close, you can get on the train in edinburgh and be in glasgow in under an hour. there's an awesome hands on science museum in glasgow. but there's lots to do in edinburgh too. I suggest googling it and seeing what the edinburgh tourist board says.
remember the weather may not be very good that time of year, but otherwise rent a car and get out to the countryside. my kids have loved our holidays in scotland, driving thru' country lanes counting sheep and cows and watching the harvesting (that's more in august sorry). And if you want to have a day off send the parents to the art galleries!
i don't know about staying there, but the apartments tend to be good sized i'm sure there are places to rent. again I'd say go thru' the tourist board initially for more info!
good luck!

If you do a google search, or if you just go to the VisitScotland.com website, you'll find loads of self-catering flats available.  Keep in mind big events like the Tattoo and the Festival and all that, because it can seriously affect availability, and also prices are often higher during those periods.  Also, keep in mind that if you're staying anywhere along or close to the Royal Mile, places are probably going to be fairly small.  That wasn't a problem when my boyfriend and I went last April, but I'd recommend making sure there are good photos of the property available.

As for stuff to do with preschoolers, I'd definitely recommend the Edinburgh Zoo.  It's a very nice zoo, and they do some good programs.  Don't miss the penguin parade!   Beyond the zoo, though...I suppose it depends on your kid.  Would s/he think castles and museums are really cool, or be bored stiff?  Would s/he be able to keep up on one of the walking tours?  There are a couple of other things that my boyfriend and I didn't see- the Dynamic Earth science centre, the Loch Ness Experience (some kind of 3D film)- that might be of interest. 

The National Museum of Scotland has all kinds of stuff in it that kids might like.  There's a big train engine and other kinds of moving exhibits that kids could be interested in.  Attached to it is the Royal Museum (I think?) and that has some hands on stuff like a robot, a rocket, etc...

There's the Edinburgh Zoo, which does a penguin march every afternoon.  We're taking our little one tomorrow. I've not been yet, but it looks good. Edinburgh Castle is pretty good, not much there for kids, but hey, it's a huge castle, so that in itself is pretty fun.  I read about something, but can't remember it now... something about a big spy glass? Maybe someone knows what I am talking about and can chime in.

There's the Edinburgh Zoo, which does a penguin march every afternoon.  We're taking our little one tomorrow. I've not been yet, but it looks good. Edinburgh Castle is pretty good, not much there for kids, but hey, it's a huge castle, so that in itself is pretty fun.  I read about something, but can't remember it now... something about a big spy glass? Maybe someone knows what I am talking about and can chime in.

That's the Camera Obscura I think, which isn't far from the castle.  I've actually never been to it but it looks pretty cool!