DH has a theory

ASmallWonder

He was chilling with the littlest and said "You're awesome.  The other one hates us unless we're giving him stuff."  He thinks kids start to suck around age 2/3 in case there's a sibling in the works.  It's nature's way of ensuring you find a reason to prefer the baby since every parent ever fears not loving their second kid as much as their first.  It's a solid theory.

NotSharknado

Agreed.