Their parents invested wealth for them but they did not pay zakaah on it. What should they do?

No File Exists
Check below answers in case you are looking for other related questions:
Paying zakaah from a child’s wealth for past years
Detailed discussion of zakaah on shares

No File Exists
Related Answers:
Is it permissible to pay zakaah in advance on every sum of money he saves?
Which is better - giving zakaah openly or concealing it?
Buying zakaah items after giving them to the poor person
Paying zakaah from a child’s wealth for past years
Detailed discussion of zakaah on shares

Recommended answers for you:
Are Tattoos Haram in Islam
Ruling on making du’aa’ in languages other than Arabic in the prayer
Is it permissible for husband and wife to remove their clothes when sleeping? What effect does that have on tahaarah (purity, cleanliness)?
Ruling on fasting for pregnant women and breastfeeding mothers
Ruling on drinking beer