My personal (and not researched) impression was that, for most common words, it comes naturally. Some rarer words (tentacule, e.g.) are an issue for children and adults alike.

One possible exception would be words which begins with a vowel, for which most determiners are written (and often pronounced) the same whatever the gender. In that case, kids might get them wrong for longer.

French children are immersed in french language from their very first day. They listen to fairy tales that their parents read at night before sleeping, they watch TV, they ear adults speaking.

They always ear ma/ta/sa/la/une chanson, and never mon/ton/son/le/un chanson. They have no reason to associate chanson with incorrect gender.

If, like french children, you spend three or four years in a french-only environment, I bet that you won’t struggle with gender anymore.