AnswerThere are plenty of safe birdhouses that your children are able to make. Any craft store like Joann's or Michael's offers pre-made birdhouses that your children can paint and decorate. Or, if you are looking to make one yourselves, you can use safer materials, such as cardboard. Also, there are plenty of free instructions here: http://www.birdhousevillages.com/freebirdhouseplans

AnswerI have never heard of a bird making a nest in a bird bath. I believe they only make nests in trees. I wouldn't worry about a bird making a nest in your bird bath. It's more used as a decoration.