I was eight when my younger sister was born. My grandma took care of my older sister and me while our mom was in the hospital (C-section) and my dad was at work. I wore my hair in braids at the time, so my grandma did her best to style it the same each morning, but she never got the braided part far enough down, so I went to school with a big hunks of braid-frizz below the rubberbands and bows.
It is not up to grandmas to know how to style hair in the current fashion. That’s for moms and dads (and friends and siblings and cousins and maybe aunties) to know. Your son needs to take that remedial hairstyling class, not you. Grandmas just need to be huggy and lovey and share what they do know. You don’t even need to know all the characters in “Frozen”. The grands will enjoy educating you on all things current.