I was very young so I would say a mid to late 90's movie. I remember something about a portal to another world in a kids' backyard. Several kids are involved. Something about a fort or tree house maybe. Something about a creature with a long tongue grabbing some kid by the leg and there was a magic crystal. May have also been some flying creatures...(may have come out of a TV?) There is a good creature I think and the kids help free him from capture and then at the end I believe the tongue creature is taken away by some guardian creatures or people and they go down into the ground and the portal is closed.
At first I thought it was 1987's The Gate or the sequel that came a few years later, but after having watched both of them I can safely say no, not what I'm looking for.