Being nearly four years old, she was certainly a child: and children are human (if one allows the term "human" a wide sense): but she had not altogether ceased to be a baby: and babies of course are not human - they are animals, and have a very ancient and ramified culture, as cats have, and fishes, and even snakes: the same in kind as these, but much more complicated and vivid, since babies are, after all, one of the most developed species of the lower vertebrates.
In short, babies have minds which work in terms and categories of their own which cannot be translated into the terms and categories of the human mind.
It is true they look human - but not so human, to be quite fair, as many monkeys.
Subconsciously, too, every one recognizes they are animals - why else do people always laugh when a baby does some action resembling the human, as they would at a praying mantis? If the baby was only a less-developed man, there would be nothing funny in it, surely.
Possibly a case might be made out that children are not human either: but I should not accept it. Agreed that their minds are not just more ignorant and stupider than ours, but differ in kind of thinking (are _mad_, in fact): but one can, by an effort of will and imagination, think like a child, at least in a partial degree - and even if one's success is infinitesimal it invalidates the case: while one can no more think like a baby, in the smallest respect, than one can think like a bee.