Ok, so I have talked to people who say they know what I am talking about but no one seems to remember the name of the show. Or maybe it was a movie? There were kids, probably teenagers, and they would go into this tree house. I believe they had a car that flew and in one skit they are in a green grass field (park) and would be chased by the purple people eater as they sang the song. Does anyone remember what this could be?

I totally remember this - it's called The Great Space Coaster. There was also a character (Gary Gnu?) who did the news, he had a line 'no gnus is good gnus'. Loved this show when I was little!

Perfect. I actually found this a few minutes ago while searching. I used to love this show!