It will probably be a bit chilly, but warm enough you can enjoy yourselves. Plus, at the Beach House at the HHead Resort, you can walk the beach and use the wonderful pool!
we were there the first week in may in 2006. for me personally the ocean was too chilly but not for my DH. my DD and I found that we preferred the pool. although the low tide left one of those shallow pools of water between the ocean and the beach and becuase it was shallow it was much warmer and my DD had fun playing at the edge of that. (and since she was only 3 at the time it was much better for mommy's sanity than having her at the waters edge...LOL) the plus is that the weather was just plain beautiful (warm but not oppressively hot). we are heading back this year --it looks like we will miss you by a week as we arrive the 11th. enjoy--its one of our favorite non WDW vacation spots.