I live within walking distance of the Hilton and Conrad on Fort Lauderdale Beach. During most of the year, they are great for families. But, during Spring Break the beach area is not someplace you'd want to take a 9 year old. Chances are strong you'll see college kids flashing something. And most of the Spring Breakers will be drunk most of the day. Last year I was walking along the beach and saw college kid throw up in the street. It was a little before 10am.

In Florida, Spring Break lasts for 3 or 4 weeks because different schools take different weeks off. You may get lucky in that your week off is different from the party schools' week off. Since it's hard to know exactly when the "bad" weeks will fall, I'd avoid Fort Lauderdale Beach altogether.

I haven't spent a ton of time in Deerfield Beach. It will certainly be less crazy than Fort Lauderdale, though.