I use Minwax Polycrylic sealer on mine.Have had no problems with it.I usually try to put at least 3 coats on.It is water based and brushes clean up with water.I use it on the birdhouses that are hung outside also and have had no problems.

Thanks for the info Lillie. I'll have to give it a try.

Most finishes do have an odor but that should mellow out in a few hours. If you need a finish for outside birdhouses try Helmsman Spar Varnish.Lots of stores carry it - Walmart, Home Depot, etc. If you are using it for indoors I like a really heavy gloss finish (makes it look kinda like ceramic) I use FolkArt HiGloss Finish, spray on.

Like Lillie 1441, I use Minwax Polycrylic on my inside pieces. I have found that it doesn't turn the whites in my paintings yellow. And, yes, the water clean up is great.
For outside work I use the Sparurathane. Although you get a strong odor in the beginning...the smell does fade away pretty quick.