Q: Is it good to give a child a second name? Can this be done when a child is not a baby anymore?
A: Give one name of a deceased close relative of yours if the name had an upper root of a middle line from the Torah, or any other name from there. That is quite sufficient.
I don’t advise giving children random names designating objects of nature and the like as is fashionable today. One’s name should correspond the name of a sacred Partzuf.