Baby hat and mittens size

so my mom asked me to make a hat and mittens for her boyfriend’s grandson for christmas, at the time he’ll be 18 months. I really don’t know enough about babies to have any idea what size to work with, and when i asked my mom her answer was “i haven’t had to worry about baby clothes in 22 years, ask someone else”. I’ve found patterns for 2 year olds but that seems like it might be big.

Generally, baby clothes are sized by age, so if you found a pattern for 18-24 mos. that would probably be the right size and have some wiggle room in case he’s a big boy. Depending on the pattern, 24 mos. and 2T are about the same.

Babys have surprisingly large heads relative to the rest of them. here’s a chart of appx sizes and a hat calculator.

There are a ton of free mitten patterns, too. Unfortunately I can’t find a hand length size page. :??

I suggest going with a pattern that seems slightly big as I just made a 6month pattern for 4 month old twins and they were too small - had to quickly turn around and make 12mon hats for them