How to frost cookies that will be mailed?

My cousin is four and he LOVES receiving mail! I decided for Christmas I’d send him a little package full of kid stuff and some home made cookies (I bought some cute christmasy cookie cutters :) )

ANYWAY. The question is… is there a way for me to put frosting on these cookies? They’ll be stacked on top of each other in the package. So I’m curious about whether theres a frosting that can dry quickly and not “smudge” while packaged.
Thanks a lot in advance :)