Ok, just spent 2 hours on this.
It is BOTH backswing and forwardswing.
They both have to read perfect. There is an easyish way.
Settings > Game Settings > Difficulty Level: TOUR Pro
Game Modes > Tiger Legacy Challenge > TODDLER YEARS > 1982 First Hole in One (very bottom)
Now you'll usually get 1 of two caddy tips. Either 5 Iron, or 5 Wood. I found the 5 wood the best.
Swing Back, hold for 1/4 of a second and then go pretty fast forward. As you are a toddler then the swing style is a lot more forgiving as it is a lot harder to overswing.
The line of swing makes no difference, you want it to read perfect back, and perfect forward.
You get 5 attempts per load. so if you haven't had any perfect/perfects after 4, just restart event. If you get any, play to the end and bank them.
The achievement pops immediately you get your tenth.
It has to be done in one session. You can go play a match, but don't change the difficulty, or dashboard.