Can't say for sure, since I wasn't there, but if there were adults being de-planed with an upset child, my first guess would be that the child had been too upset to sit in his seat and was too old to be a lap child. I was once on a flight that lost its turn to land because a toddler threw a tantrum and wouldn't sit in his seat to land. Because he was too old to be a lap child, we had to circle till the tantrum passed. Of course as soon as he was under control, ATL closed for weather and we had to circle for 45 minutes

Kids can be pretty unpredictable!