Another vague memory of a film from my childhood, I remember I boy going through the larder or maybe cellar and finding that lots of food and boxes had been nibbled at so goes round putting mouse traps. In the end he finds it is this weird ping pong ball type creature which at one point he puts in a bowl of custard and the ping pong ball slurps it all up. I think it turn out it is an alien that got left behind or something and a ship comes back to pick him up at the end

Sounds like Glitterball (1977)