Trying not to repeat any that were mentioned, so all I got is
Clerks
everything by mel brooks. (think I saw blazing saddles and young frankenstein, but he had more gooduns like history of the world and the producers for instance)
The Good, the Bad, and the Ugly
Outlaw Josie Wales
Pick 1 or 2 John Wayne movies. They were all good but not worth watching them all IMO.
Deep Throat
Debbie does Dallas
Monty Python's search for the holy grail
Monty Python's Life of brian.
Monty Python's Meaning of Life but only if they really liked the other 2.
South Park Movie
White dog
Cujo
Airplane and as many of the sequels as they want
Naked Gun. NG1 only. No matter how much they beg to see 2.5, don't do it.
Also, they need a good diet of the B movies that Elvira and MST3k used to show. Can't think of any of the names right now.
along the same lines, Cabin Fever. It was so bad it was good.
As you can tell, I don't care about your kids. You decide when they're old enough for each movie. Damn, this list turned out longer than expected.