I first watched Mad Monster Party when I was a wee lad. I loved it then and still love it now. If you haven't seen it then I would urge you get hold of a copy and watch it. Glorious stop motion (or "Animagic") from Rankin Bass. Mad Magazine and EC Comics artist Jack Davis designed the characters. Also, a sequel was made (the year I was born... again, it'd freak me out if it was the same month, same day etc), which was done in 2D and was called Mad, Mad, Mad Monster Party, though I've never seen it.
Whilst on the subject of Mad Monsters (the mention of sequels has reminded me), I have a children's book recommendation also, especially if you're a fan of things Frankensteinian and Universal Horror. A book called "Frankenstein's Aunt" by Allan Rune Pattersson, in which Hannah Frankenstein (a wonderful character) visits her nephew and decides to put things in order at Castle Frankenstein. A lot of fun. The reason I say sequels is because a few years ago I managed to track a copy of the book down (it was a favorite from my childhood) and discovered it too had a sequel called ... wait for it ... "Frankenstein's Aunt Returns" (which I have since acquired and read) which serves as a direct sequel to the first book, in which Doctor Pretorius and Doctor Frankenstein create a boy named Franklin. Fun, but the first outing was pleasantly pocked by nostalgia for me. A fun return all the same. There was also a TV series (seven episodes in all) made in Sweden in 1987 and starring Viveca Lindfors as Hannah (though I've not seen that either... apparently the series was recut into a movie called Freckled Max and the Spooks).