I've been thinking mostly about actual paleolithic children rather than modern-day equivalents. I imagine they got a decent supply of breastmilk, but can't imagine they then started in on pureed vegetables - whatever your stance on carbs is. What ideas or evidence do we have for how children used to eat?
I can well see that an addiction to sweet food, breads and cereals, and general fussy eating can easily be produced in a world where these things are available and permissible. Did they just start nibbling leaves? I can't see how that would be a great step forward for development over milk. Surely they must have been getting involved with the animals sooner or later. Were they tearing into juicy bits of liver (for a good ol' vit A overdose)? Did they subsist on sucking the blood out of bits of meat? Did they just breastfeed until they had the teeth to tackle the meat directly? Are the rules basically the same as for adults? Make the right foods available and let them figure it out? I'm sure we must have some idea what the historical situation was, but how does it fit with the science, and what do you do in a world where you can't hope to stop other people feeding your child foods which might set off a life-long dysfunction?