Are they kids or adults?

I was trying to figure out if the voices of the animals in the Backyardigans were kids or adults. They voices of the animals seem to be childish. They also seem to be not as whiny as children's voices tend to be. Usually when I have to listen to a song where children are singing I get really annoyed. The kids on the Backyardigans sound pretty good for kids but not good enough that they could be adults. Maybe they are kids that just had their voices altered so they aren't so annoying. That would be an awesome job for a kid. I wish my nieces and nephews could sing so they could do something like that.