Well no I don't think it is selfish. Someone has to raise the next generation. Unless you feel it's OK for the human race to die out, I suppose some people do genuinely feel that, I don't. I quite like humans and would like us to continue! I don't especially think my child will do anything enormously earth-changing, but I do try to raise my children to be kind and considerate people and I believe that they will do good in the world, as I try to do. Lots of little incremental positive changes over time.
You could just as easily say it's selfish to not have children, because you're leaving the hard work to somebody else. I don't think that's true either - having children is hard and not something anyone should go into lightly. If someone doesn't want children then they are probably better off focusing their energies somewhere else.
I just don't think being selfish or not comes into it. I didn't have children only for my own benefit, although of course I thought I would benefit from it, or I wouldn't have had any! That's the same for lots of things you could do, though, and generally a good thing - you will tend to do better at something if you enjoy it.
Is it selfish to work in a job you enjoy because you enjoy it, when you could be using your education and skills for some worthier purpose? What if the job does some good, but it isn't the best possible job you could do for humanity? I don't think anyone would say that about work so I don't see why people say it about children.