This was one of the Muppet fairy tale specials produced for television in the early 70's, and from what I've seen & heard, the best. Although the only other one I remember seeing is "Muppet Musicians of Bremen", which I must say I didn't find to be all that great (as a child or adult) but boasted some nice and innovative puppetry.
"Frog Prince" however, is quite remarkable. Like the other Muppet fairy tales, Kermit the Frog hosts this but actually plays a big role in it as well. Other now-staple Muppet characters, Robin the frog & the giant Sweetums, make their debut here. The puppetry is again fantastic, and the Muppet performers do such a great job, you'd hardly know most of the characters here are made up of only foam, fleece and fur.
Overall, this is a great special you should definitely share with your children. Without a doubt the best rendition of the Frog Prince I've ever seen.