That is certainly a slew of them, and there's nothing wrong with considering close friends' children as family as well. We've got a handful of those around my family, too. Were most of them at that birthday party? It looked like a large, close-knit bunch.
How much land does he own? Is he the one that owns the park? I know it's privately owned and maintained but open to the public. One of my sisters live near there, and her kids insist it's their favorite park.
Not a problem at all. Is he teething still or just enjoys putting everything in his mouth?