This is on the fairground level (just after the race). You will have a big battle with colorful bear toys in the background. Afterwards you will see a crying woman on the right side of the screen. Stop here and switch to Terence or you have to restart the entire level!
There will be a cutscene where woman asks you to help her child stuck on the carousel. Don't do anything for a minute, achievement unlocked (if you play Bud, Terence will automatically help the girl).