Landmark visitor centre's a good day out. Sorry can't do links. Also the osprey place just outside Aviemore, although I don't know if they'll be there at the end of May. What age are your children?

Try here for ideas

\link{http://www.kids-scotland.co.uk\kids scotland}

LAndmark was great - a good combination of worthy forest stuff and some out an out kids' entertainment - slides swings etc.
The ospreys have already arrived and there is a chick.
Loch Morlich is good if it's a nice day - it even has a beach!

Take the funicular railway to the top of Cairngorm
If you fancy a drive - the beach at Nairn is great - very 1950's holiday - we played crazy golf with the children - they loved it. Onthe way ther I would reccommend stopping off at a place called Logie Steading. It's got a great play area - and the best cafe ever - they even do wholesome children' slunch boxes... and the cakes are to die fro. There's also an art gallery and a second hand book shop.

we went there last about 18 months ago so I hope it's still theer.

Also a good place to eat was in the High Street of Grantown on Spey where they did lots of options for children and colouring too - but not in a naff way!!
Yikes i can't remember the name - but it always has some balloons outside!

have a fab time.

Landmark is really good. Also the steam railway from Aviemore. Boat of Garten osprey centre is good - the ospreys are sitting on eggs at the moment so is a good time to visit - end of May there may be little ospreys! Also Funicular up Cairngorm mountain, though if all the ski-ing is over then you won't be able to go onto the mountain at the top, but the Ptarmigan restaurant is good.

Also, the Highland Wildlife centre, down the A9 a bit is lovely. And the Black Isle wildlife centre just beyond Inverness is lovely as well. Dalwhinnie distillery is good, but maybe not for kids. There's a lady by Loch Eilen who does pottery - on certain days you can try throwing a pot and she will fire it and send it to you - she's lovely. \link{http://www.hie.co.uk/businessdetails.html.bid-3329.html\details here}

Landmark is great! There is a fantastic forest walk on a wooden boardwalk that take syou up through the treeptops (abd red squirrels at the end!) There is also the water ride which your 2 eldest will love, a climbing tower, good play equipment etc etc.
Near Aviemore there is a wildlife park (poured when we were there but looked good)
The Cairngorm mountain railway is worth a trip.
My 6 year old also did sledging on a dry ski slope (again near aviemore) which was great.
There is loads to do but it can be quite pricey.
We thought the restaurants in Aviemore were overpriced and not up to much.
If it pours with rain, there is a soft play place, including indoor mini golf, at the Coylumbridge Hilton which is open to non-residents.

Ah yes, I forgot teh Hilton in Coylumbrige - we used their swimming pool one day when it was raingn ( we did pay!!!!!)

We also hired bikes an cyled around Loch an Eilein - baby seats were provided.

\link{http://www.penspots.co.uk/\this is the pottery place} - she really is lovely, just has a little workshop in the middle of Rothiemurchus forest. Definitely something to support, and the kids will love it!

The place to eat that Finbar mentioned is called JJ's. They are very friendly and extremely good with kids (including running out of kitchen with basin when dd started throwing up everywhere!)

The website for Landmark is \link{http://www.landmark-centre.co.uk<a class="break-all" href="http://www.landmark-centre.co.uk}" rel="nofollow noindex" target="_blank">www.landmark-centre.co.uk}

There is also a new swimming pool in Aviemore with flumes and a wave machine (not been yet so can't personally recommend it)

Everybody else has mentioned everything I can think of :)

Hopefully the weather will be nice so the kids can play on the beach at Loch Morlich. Also great for kite flying if windy.

Highland Wildlife centre agree it is good, don't miss the walks once you have driven round and parked the car there a re a few walks that take you round some more enclosures on foot, with different types of habitats.

WE went to the landmark centre after a mumsnet recomendation and dd absolutely loved it as did we. Highly recomended.