Sidequests

This is a Masterlist of all the sidequests in the game (Plus their solutions):

Pink Haired Girl Sidequest
Location: Past The Mahai Mountains

You'll see a Pink Haired Girl walking in place, Talk to her and follow her

Reward: 1 Gem Shard

Hide and Seek
Location: Castle Town

You'll find a group of 4 kids talking, Talk to one and say "Yes", Go look for the group (See Answers, Does not matter what order), Once you've found 3 of 4, a small cutscene will play, then go into the Item Shop and talk to the girl behind the other person in front of the Girl's Restroom

Reward: 1 Gem Shard

Trade 'ya!
Location: Ent

Go into the different houses (Shown in Answers) and talk to the npcs (IN THAT ORDER)

Reward: Gem Shard