Little boy biting

Hello, I am posting on behalf of a friend who is at her wits end with her
little boy biting. He is just turning two years old and will bite other
children every now and then as they are playing. He doesn't seem malicious
about it just goes up to them and bites them, in other owrds it's not
usually sparked by a conflict. He knows he's done something wrong afterwards
and says sorry but it doesn't seem to deter him from repeat offending :-)

Umm what else, Oh yeah he has a newish baby sister (4 months) and may be
teething (red cheeks, drooling, grizzly), I can't think of anything else
that might be relevant off the top of my head.

Any advice would be greatly appreciated.

Thanks in advance

Judy