In 18:4 it says "ושם האחד אליעזר" - the name of the one is Eliezer. Eliezer was the second child, so why does it not say "the name of the second was Eliezer"?
Even though in the order of children he was born second, but Eliezer was not "second" to Gershom in any respect. The Torah gives equal importance to both children, to both Gershom and Eliezer.
We should treat all our children with equal respect and not treat was as "number one" and another as being "second" No child should feel as if he is second class.