Young Frankenstein has more double-entendres than you can shake a dead man's arm at, and with all the schwanstucker business, there are plenty of (very big) single entendres too. Mel Brooks isn't really known for subtlety.
This is all in good, not-exactly-clean fun, until the monster kidnaps Elizabeth. In a horror film, this scene would be an exceptionally horrific rape scene, but Young Frankenstein plays this situation of dubious consent for laughs. You can explain that to the kids.