I don't remember a lot so there is prob no hope in me finding the answer!

It was a cartoon I use to watch when I was a kid... I think it was a movie perhaps.. either way it was an animation. I grew up mid 80s to 90s seeing it so it would be from around that time, maybe a little earlier even.

There was a boy and a girl (bro and sis I think) and they here these little creatures/men outside their house and go to see them and somehow end up underground if I recall in their world and someone is in prison (maybe one of them gets captured) so they have to break them out, find the key or something.

And these creatures/little men sing but its not really singing it more like making these funny sounds in a tune. It's a funny sort of sound, perhaps like a croakish kind of sound.

Not a lot I remember besides that so any help would be greatly appreciated,
I'm going insane!!

THANKS!:confused: :)

Well, don't get your hopes up, because I this seems too easy. BUT that (with a few conflicting details,) sounds like Ewok Adventure. The brother and sister' s spaceship crashes though, I think. The Ewoks find them, but their parents get captured by this giant and they have to go break them free.
Just thought I'd throw it out there. Good luck.
SORRY, I just realized you said it was a cartoon. I have no idea

Was it "A Troll in Central Park"?

Fraggle Rock