Latter half of May is usually real nice up in New England, BWI flights are cheap to Providence or Manchester. Check out cape cod, or bayside-inn.com

If you are going to Delray, I have a couple ideas. Single mom and my son is seven now so we have done it all. There is a great children's "Schoolhouse museum" in boynton which is the next town up and has a great playround. Veteran's park is on Atlantic avenue and intracoastal waterway in Delray has an fun playground and you can look at the boats. If you have a car there is the Palm Beach zoo, Fort Lauderdale Science museum, Lion Country Safari, malls with indoor playgrounds if it rains, my son likes the observation park at the Palm beach airport (easy to please).