Child's Last Name

I am due with a baby in April but I want to give the child my maiden name to go with my other child can I legally do that even if I do not use my maiden name any longer?

You want to change your older child's name? (If not, why did you post in the name change forum?) Where's the father, is his paternity established, and what's his position on the name change? What state's law is involved?