If the little tyke is not authorized to attend the flagstick before another player makes a stroke, he is subject to penalty under Rule 17-2 and the player does not incur a penalty. A putt that strikes the flagstick would be canceled and replayed.
In all likelihood, though, the player is aware that he is attending the flagstick. If there is no objection before the stroke, the player is deemed to have authorized the attendance. Any breaches of the Rule fall on the player – clearly the more responsible party!