Como dizer "Criança de colo" em inglês

I gave up my seat to a mother carrying a baby. ("Up" is common but not necessary.)
I gave up my seat to a mother with a baby in her arms.

I have given up my seat to a lady carrying a child.
I gave up my seat to a woman with a child.
I got out of my seat so a lady carrying a child could sit there.

A literal translation may be "babe in arms". Surprisingly, however, the term is often used to mean "someone inexperienced, innocent, ignorant of the ways of the world, someone too inexperienced to handle the responsibilities of his position".

You know nothing about politics. The public will eat you alive. You are just a babe in arms.