Something unexpected I felt when holding a baby

Since I don't have children yet, I rarely have the chance to hold a baby.
However, when I visited a friend's house recently and held their son (7 months old), I was surprised.
Because the baby kept moving, I ended up holding him by his legs,
and I realized that babies' lower body muscles are surprisingly firm.
(My friend's son isn't walking yet; he uses a baby walker.)
I had just assumed babies would be soft all over.