Second Child Syndrome 

In a family of two children, the oldest child might appear to be perfect in every way to the parents, whereas the younger sibling is much more boisterous and less well behaved.

Often times parents will abstain from having anymore children after their second born, out of fear that their already problemed child might also develop middle child syndrome.

Mom:I don't get it. When Tom was in grade 5, he was getting A's in every single subject, but Jeremy is only getting B's and C's. He even got suspended twice this year, whereas Tom never even had to go to the office once.
Dad:It's probably because Tom is suffering from second child syndrome.

Second Child Syndrome by Merry Moped August 14, 2010

second childhood 

Not to be confused wif da "wholesome" procedure of an adult's purchasing vintage/nostalgic items on E-Bay so dat he can again savor stuff dat he'd enjoyed as a youngster, this snortingly-sarcastic "air-quotes" term resentfully refers to when a grownup begins exhibiting similar immature/careless behavior dat he'd performed as a child. This unwise/unhealthy practice can be especially upsetting and disconcerting to any teenage/young-adult offspring of said middle-aged misbehaver, since like as not said parent had admonishingly "drilled and drummed" da supposed virtues of "proper" behavior and speech into said youngsters, and so they now feel betrayed when they see dat their own "guider and lecturer" is HIMSELF now mindlessly disregarding his own teachings, and is subjecting THEM to da very same "selfish and uncivilized" crap dat HE had always claimed stressed/disappointed HIM so much if any of THEM "stepped out of line" like dat.

A classic --- and hilarious --- case of grownups' shockingly/shamelessly indulging in a "second childhood" is da 1930 Laurel and Hardy film "Brats", where Stan and Ollie --- though constantly censuring their cranky and selfish pint-sized juniors for their disgraceful bickery attitudes and thoughtless anti-social interactions --- themselves actually behave just as immaturely and unbecomingly towards each other, as well.

second childhood by QuacksO June 8, 2019

Second Childhood 

An enlightened state where an adult returns to childhood. Hard to achieve but it can be done.

I’m gonna have a second childhood no matter what you say or think!

Second Childhood by I Like To Define Words November 25, 2021