Hi Rachel, What a fun Birthday celebration for your son!
I would recommend that you stay in one of Disney's Value Resorts with a 7 year old boy. If he is a Sports fan, he would enjoy All-Star Sports. If not, you may want to look at the Pop Century Resort.
As far as visiting the Parks, I'd suggest that you check out the calendar on Disney's website for the dates that you will be vacationing. Click
HERE to view the Magic Kingdom calendar. Switch it to May, and then click on your specific dates. That will show you the Park hours, parades, fireworks, etc. This way you can best plan your trip. You'll want to view the calendars for Epcot, Hollywood Studios and Animal Kingdom as well.
I would recommend a Park Hopper Ticket because you are only there for a limited amount of time. This way if one Park closes early, you can move on to the next one.
For his Birthday celebration dinner, I suggest Chef Mickey's. See
HERE. They have a great, "Make your own ice-cream sundae" station that my kids love. The buffet is wonderful with lots of kid friendly options available.
I recommend the standard Disney Dining Plan, as your son will be able to eat for under $12.00 per day. However, because it is so close to May, I would be certain that you are able to secure Table Service reservations first before buying the Dining Plan. You can call 407-WDW-DINE to see what dinner options are available this close to your trip.
Due to space constraints, if you would like to send me any follow-up questions, I'd be happy to assist you further.
Thanks and Happy Birthday to your son!
Kaylene