Both are fine. The choice depends on what you actually mean. Both of them imply that "bewitching" is an event that happened at a time in the past. He bewitched the children at some specific time. Perhaps he cast the spell on February 29th, 2018 at midnight. The act itself is over. The effect of the act may or may not have continued. If you say "he bewitched the children," we do not know from the statement whether "bewitching" has a lasting effect or not. That is a matter of our real-world understanding of bewitching. If you say "he has bewitched the children," that implies that the children are still bewitched. It implies that it had a long-lasting or permanent effect. If you say "he cleaned the bathtub," maybe he cleaned it this morning and it is still clean, or maybe he cleaned it a week ago and it has become dirty. If you say "he has cleaned the bathtub," that implies it is still clean.

For me, it would sound better to say: The children were bewitched by...