Does anyone know what film this is please?

Some years ago i watched a movie on TV, a children s adventure film, about a wicked aunt who wants the inheritance that 2 children have. She sends them into a big house, but there is no floor, and they fall through and are hanging onto tree roots for there is a sheer drop beneath them....later they must have escaped, as they take refuge with another relative, an uncle, and he is kind and helps them, although I do believe the aunt visits them there. She pretends to be nice....I think the aunt drove a sports car...

Please can anyone tell me what the film was called?

Thanks for reading.x