system
Given the following post, respond as if you're commenting on Reddit:
human
[ATLA] Does the new avatar have to be born the instant the old one dies?

In that case, shouldn't finding the new Avatar be relatively easy? Like the day they die, the respective kingdom would just ask their citizens if any new children were born that day and around what time they were born. This should be especially easy to figure out for smaller nations, like the air nomads. I know that Korra was considered to be discovered pretty early (around 4 years old I think?) but I'm not really sure why it would take that long. Couldn't they just do the toy test (the one Aang did) on this select group of kids born that day way earlier?
gpt
Yes, it's instant, but tracking it down is harder then it seems.

For most of its history, the Avatar world was high-medieval technology- we've only had one avatar born during an age of radios and easy communication, who was not coincidentally the one found early.

So, you need to figure out when the avatar died (not easy if they died from violence or accident), and then you need to get that date to the leaders of the relevant nation, and then they need to check everywhere. With horses.

The Earth Nation forgets one house in the slums of Ba Sing Se? Missed the avatar. Overlooked a sand bender tribe in the desert? Missed the avatar. Someone simply misremembers when their child was born, having no written records? Missed the avatar.

It is really hard to do a comprehensive survey of an entire nation when your most advanced technology is "fast man". It's easier to look out for the signs of the avatar when they're able to do avatar stuff, which only happens when they're older.