Depends where you live. If it is nice out in April where you are you can do a nice spring time cook out in the park. If it is rainy and muddy then you may want indoors. I once went to a birthday party at a Ramada INN. They gave us a confrence room to do cake and gifts in and there was a pool for swimming.
Is it warm in April where you live? If so, you could go to a park or do something outside. I went to a birthday party at a park for a 1 year old and they had one of those blow up jumpers, the kids loved it. It doesn't really matter where you have it if you plan right. You could do a theme party, like pirates or something. :)