I guess the reason why they didn't allow you inside was because maybe they felt it might be a distraction. On the contrary, it shouldn't be. They should have probably seen you as an internal support system and a motivation to your son. At least it was a good outing; a morale booster for your son.
Ya, its never a distraction , they simply denied citing unjustified reasons.
Crazy, at the end it was a decent outing for your son.