It's apples to oranges.
Modern Artificial Neural networks are nowhere near the scale of the brain. The closest biological equivalent to an artificial neuron is a synapse and we have a whole lot more of them.
Humans do not start "learning" from zero. Millions of years of evolution play a crucial role in our general abilities. Much more equivalent to fine-tuning than starting from scratch.
There's also a whole lot of data from multiple senses that currently dwarf anything modern models are trained with yet.
LLMs need a lot less data to speak coherently when you aren't trying to get them to learn the total sum of human knowledge.
https://arxiv.org/abs/2305.07759
>but it's still kinda odd we can't get to the level of a 5-year-old with just the experiences we would expect a 5-year-old to have
Well we're not building humans.
"It's still kind of odd we can't a plane or drone to fly with the energy consumption or efficiency proportions of a bird".
I mean sure I guess and It's an interesting discussion but the plane is still flying.