What's wrong with this sentence?

[Juliam]

While Charlies parents were pleased with his grades, they still found a plethora of picky things; to nag and torture their only son with.

[Boadicea]

The possessive 's (genitive) is missing in 'Charlies parents'.

It should be Charlie's parents

[RonBee]

While Charlies parents were pleased with his grades, they still found a plethora of picky things; to nag and torture their only son with.

It's his parents that were picky, not the things they nagged him about. Try:

Although Charlie's parents were pleased with his grades, they still found many things to nag and torture their only son about.