Not Spanish, but my ds used to watch French cartoon on youtube, and learned to sing cartoon songs from you tube as well. Maybe there are Spanish version of popular children's cartoons on youtube as well? Now he is older so uses online language site, but still watches and sings songs.
What do you use to teach your kids Spanish? Are there any good TV program or games I could get? He picked up numbers, colours, days or the week, and basic greetings without actually being taught so I'd love to expand that. I just don't know how.