Coming in early May was a good time. They were booked up on the weekends, but were fairly quiet during the week since school is not yet out.
Their dog park is one of the best I've seen. Lots of things for kids and adults to do.
The closest shops are in Berlin. Don't forget to stop at Crabs to Go to get genuine Maryland crabs.
The Assateague horses were great to see. Rehoboth is one of the dog friendliest towns I've seen. Every outdoor seating area allows dogs and even has water bowls for them.
Note: If you head down to Chincoteague to see the lighthouse, leave your dogs at home. They don't even allow them in the car.