Describing how children learn language as "memorization" is probably not accurate. Native speakers do "learn" rules, they just do it more or less unconsciously because our young, developing brains are wired for language acquisition.

I think this has far more to do with the difference in how children and adults are taught languages than structural differences in the brain.

After all, 2 year olds aren't sat down with pages of conjugation tables to memorize, rather they pick things up from speaking and being corrected.

I think you missed jinushaun's point: you can learn 70-99 in French without rules, just like you learn 0-19 without rules in English.