system
Given the following post, respond as if you're commenting on Reddit:
human
eli5- Why and how are babies so strong? What advantage does having a strong core give babies?

I’ve read a few things in the past that say that babies pound for pound are stronger than bulls. Also they seem to have ridiculously strong cores (abs) without training. Plenty of videos show them being able to hold their legs up over grass for large amounts of time when they don’t want to touch it. How are they able to achieve this without training? What advantage does this give them if they can’t naturally cling on to mom or dad?
gpt
This is explained by the square-cube law. In short, strength and durability are proportional to the size squared (X*X) and weight is proportional to the cube of the size (X*X*X) so if you take a human and shrink him proportionally to half size, he will become 4 times weaker but 8 times lighter, so in total it would be twice (8/4) as easy for him to lift his own body.

Babies have different proportions and their muscles are less developed, of course, but still they are much smaller than adults so it's easier for them to do these tricks.  Babies appear to have lots of strength, but it's realistically only in relation to their size.

They are super good at clinging to their parent.  Their strength doesn't "go away" as they age, it just doesn't grow proportionally to their size. They do get stronger as they age, but they get a lot heavier too so some of that "innate strength" (and the strength they gain) goes towards just lifting their increased bodyweight rather than feats of strength like holding their legs up easily.