My son (also a July baby) had a birthday last year he was prep so didn't quite have the same issues as a kinder group. I had it at our local Leisure Complex (I live very rural so couldn't have it at my house) it was quite reasonable in price as I supplied my own food so I was only paying for the hostess and the room.

I ended up only inviting boys my son had 2 girls he wanted to invite but I felt they might have been uncomfortable amongst 10 boys. If it was more even in numbers I wouldn't have minded. That being said it worked well with the all boys, they had there laughs and boy jokes.

At my sons kinders there was several parties where only some kids were invited, like another post the invitations were placed in the pidgeon holes above the lockers so as a parent I didn't make a big deal of the invite in front of other children.