Should I require an apology or “I’m sorry” for hitting others?

The short answer: No.

An apology is not as important as mending the interpersonal connection. If the child is developmentally capable of empathy, what would they want/need in the other’s place?

“Tommy looks sad. How can we help him feel better?”

That said, boundaries are critical here.

“Hands are not for hitting.”
“I can’t let you near the baby if you hit her.”
“Stop. You may not hit. I’m going to take the toy until you can be safe.”

The goal is not sorry, it’s repair.

“What do you think Tommy needs to hear right now?”
“How can you fix things with Tommy to help him feel safe with you again?”