Adult child 

Someone who is an adult (over 18) but still displays child-like features and characteristics. They feel as if they still are a child and don't want to grow up yet, spirit wise.

Johnathan and Samantha would rather play video games and go go-kart racing than go on sit-down dates at fancy restaurants. Thus, they are adult children.

Adult child by KingKidnem September 16, 2017

Adult Child 

An adult child is someone who is between the crisp ages of 18 - 24. College age. The average adult child is foolish and frequently drunk.

Plural: Adult Children

'Ugh, he's such an adult child. He can't even pay his rent. He spends all his money on crack and alcohol.'

Adult Child by Bingus Aran January 2, 2022