When Japanese kids first start talking, we only use Tameguchi with everyone - our parents, friends, and even strangers.
No need to stress about being polite or rude, life is pretty chill and simple 😎
But when we start going to kindergarten around 3 or 4 years old, we learn to socialize and meet our first Sensē (teacher)!
That's when we start learning to speak politely.
For example, when we greet our teachers or adults, we're taught to say Ohayō Gozaimasu (good morning: formal) instead of just Ohayō (good morning: informal).
As I said, we use Tameguchi when we talk, but we're already taught to use Keigo for certain phrases when speaking to adults.
In kindergarten, we have events like sports day and Oyūgikai where we learn songs and dance to perform in front of our parents.
A few kids are chosen to do opening and closing speeches and we're taught to make in Keigo.
It's not like we're giving long speeches or anything.
It's just a few simple phrases but we're already expected to use Keigo in certain situations at such a young age.