“What is your opinion regarding children joining a dancing circle at a wedding or Simchas Torah? Must all the men immediately leave the circle lest they face arrest??'”
No. If the parents of a child allow them to join the dancing, than they are providing consent for the child to be touched by others in the circle. In the other instance, there was no expectation by the mother than some guy would start shlepping her child towards the door. Whatever his motivation, he exercised very poor judgement.