What kind of paint should I use for a tree house?

My husband and son are building a tree house, and my son wants to paint it when it's done. What kind of paint should we use? Also, if we use the right kind of paint, will it seal the water out? Or do we have to use water sealer as well?

I would use a coat of "Killz Acrylic-Latex Primer" (this seals it and protects it from water damage) and then use any kind of water-based paint over that.; a satin to semi-glossy sheen for paint is the best for a treehouse. I would use 2 coats of the primer then go over with an acrylic water-based paint. They have them at Ace Hardware, Lowes, or even Walmart.
And if you wanted to waste a little more money and make the tree-house bulletproof, I would throw on a coat of clear, water-based concrete sealer/clear water-based Polyurethane sealant on top of the final base coat.

***And ALWAYS ENSURE that you use water-based primer with water-based paint; and oil-based primer with oil-based paint. NEVER mix water-based products with oil-based products...or else the paint job will only last a few months at the most, especially with how crazy kids can be sometimes.

..Or what you could also do is to stain the wood to a color of your liking with a water-based wood stain (sometimes harder to find than oil-based stain) and throw a clear water-based acrylic/clear water-based polyurethane over that. It gives the tree house an "old cabin" look ;-) Have fun

Make sure you prime it before you use any exterior paint anywhere from flat , lo sheen, semi gloss. Latex primer for exterior for wood use is what your looking for. None of these are necessarily waterproof, but what you can do is get a clear sealer of waterproofer for wood, and apply it after your paint has dried. It will slightly change your color though, and you also should seal it inside and all the surrounding of the wood in order for it to work really well.

If you use an acrylic fence paint,it will seal the timber and look really good.You can wash brushes out in water.

any exterior house paint