Children's Entertainer

These can be done in the quest Mereldar's Light, which has you do three of these games and the world quest Work Hard, Play Hard which has the challenge modes available. I dropped and re-picked up the campaign quest to finish all the normal ones.
Progress counts across characters which was required as doing the challenge modes counted as 4/4 and completed the world quest for me.

Who is scariest?
There are three kids upstairs in the orphanage, I talked to them and picked Nerubian, I assume both will work.

Scary Monster
Three kids outside near the climbing equipment, talk to them and push each of the 4 action buttons.

Hit the Target
Talk to the kids in front of the target, throw a rock at it.

Tag
Click on one of the two running kids.

Floor is Undersea
For this one, talk to the kid near the fence. You need to walk along the fence, jump across the gap (there's a barrel in the middle), go around the corner again, jump across again and click the kid at the end of the last fence segment, this one took me a little bit to figure out all the jump distances. I practiced the different segments separate to the game to get the distances correct.

Hide and Seek
Talk to the kid near the doorway, you'll get a bar and pings to the hider. He was behind the orphanage for me, not sure if it's always the same.

Hide and Seek - Challenge (only available in the World Quest version)
This is mostly the same, except that now Wyllam is running around, I found him heading up the hill at 43.0, 53.3. Use the pings and location bar and you'll get there.

Floor is Undersea - Challenge (only available in the World Quest version)
This one is hard, you have to complete the course with a lot more complicated jumps and barrels in the path. The path goes halfway down the fence, across to the barrels under the climbing frame, follow the barrel path to the next fence after the gap, jump across to the next fence as normal, then jump to the barrels to get around the barrier to the last fence. Good luck, this took me many attempts.

Apparently for both the Floor is Undersea games, you can cheese it with a warlock's demonic circle, monk's transcendence or mage's alter time.

WARNING:
Do NOT do the Hide and Seek - Challenge or the Floor is Undersea - Challenge first.
If you do a "challenge" first, it will count as all 4 games

Do 3 of the normal games and make the 4th game one of the challenges. This way you can knock this achievement out in 2 rounds.

I'm about to play The Floor is Orphans with this kid.