I usually give new characters less than full xp, and then allow them to gain +50-100% xp if they died until they catch up, or +25-50% xp if they missed sessions until they catch up.
If they need a reason for this, I just say that the company of the more experienced characters inspires them.
But I play a pretty nice GM. I just want all my players to have fun.
I instead often try to increase the challenges they face, except if they really are green.