Just to underscore your point about interaction needed to learn language skills, I remember a little boy who lived locally to my workplace about 30 years ago.
It was a pizza delivery place on the edge of an estate. I worked there as a student during weekends and holidays. Lots of kids running about the streets locally.
One was about three years old. He was always on his own. One day he started running into the glass door of the pizza place head first.
He just charged at the door and let out out a yell. We rushed out to open the door to stop him hitting his head again. And he just ran back and forth.
We were worried about him as he was too young to be out by himself. It was also really cold outside (pizza place was very warm due to oven).
We worked out he was probably hungry and offered him some thing to eat. He was very shy.
The manager lived round the corner from the shop and did some discreet asking round about the kid. The manager’s sister lived close by too and between them they managed to trace him.
Turned out his parents were both heroin addicts and just didn’t look after him. At that point the manager and his sister went to social services. The sister ended up fostering him long-term.
Whilst this was taking shape the little boy would come into the pizza place quite regularly and we’d give him something to eat and he sat in the little seats by the window out of the cold.
He’d run off if we tried to talk to him too much though. And then he went to live with the manager’s sister.
After a few months the manager and I were chatting when it was quiet and he said that the difference in the kid in just a few months was unbelievable.
The manager said he thought it wasn’t just that his sister looked after the little boy, but that she spoke to him. And that the interaction was just making him unrecognisable from before.
He could ask for food if he wanted it now, whereas at first he’d just yell if he was hungry. And now if he asked for a biscuit or some juice or whatever he’d say please and thank you. And that he liked animals, especially dogs and could talk about them a lot with the manager and his family.
Obviously the fact he was fed/warm/clothed/cared for made huge difference. But it was also people taking an interest in talking to him.