It is a long way off before I have to consider him dating anyone! When he does though my main priority would be for to be dating a nice person. Someone who is kind, respectful and treats him well.
Ideally I would prefer him not to be involved with someone who already has a child but I wouldn't forbid it. Life isn't that simple.
I would treat her like any other girlfriend, if she was a nice, decent girl I would be welcoming to her and if she was treating him badly I would do my best to discourage it.
So really the personality/behaviour of the girl in question would be the deciding factor not whether or not she has a child.