I don't know anything about birds, are there different birdhouses for different species, why? I assume they use different materials and maybe build a different type of nest, but why different sized birdhouses?

It's cool to see that you are also instilling in your child knowledge to preserve wildlife. I'm still many, many years away from having a child, so, I'll take this post as a little something to keep in mind for my future and that of my potential future family.