Update: Over on omniglot.com, a commenter claims that Thai singing does use tones. This certainly could be true -I just can't hear it in the children's counting song I mention below.
I have some reservations about Barney the purple dinosaur.
I'm an educated man in my late thirties, but my reservations have nothing to do with watching a stuffed dinosaur come to life. It's not that Barney is too cute and cheery, or that I already know my shapes and colors and don't feel a need to review them.
The problem with Barney is that he sings.
I've been watching Barney dubbed into Thai with my three year old son. Overall, it's a pretty good source of input. The shows review and reinforce important vocabulary, like days of the week, numbers, colors, and shapes. Review of basic vocabulary is interspersed with easy dialog. The only problem is the singing.
Thai is a tonal language, which makes it impossible to learn correct pronunciation from songs. This is most obvious to me when Barney sings his numbers. In Barney's counting song, there are no tones at all, just musical notes. Although I'm very familiar with Thai numbers, it sounds strange, foreign, and hard to understand. There would be no way to learn correct tonal pronunciation by listening to it.
On the other hand, Barney has excellent spoken dialog, and Thai children listen to songs without a negative effect on pronunciation. The Barney input is helpful, as long as I don't focus on the songs or try to learn vocabulary from them.