Birdhouse Making

A few months ago Owen painted his birdhouse in 4H (or Forage as he calls it). He wanted to fill it with seeds and hang it in the tree. The only problem was that a 5 foot drift of snow was around this tree until just a few weeks ago. Mia got her birdhouse in her Easter basket, and spent an afternoon painting it. Dylan, not wanting to be left out, had to have a birdhouse as well. Anyone know any tricks to getting birds to actually go in them? I'm sure curious little noses and hands investigating the houses daily doesn't help.... :)