My first was six weeks old when lockdown hit. She spent nearly the first two years of her life with just my wife and I.
We always resolved to speak to her as an adult would and only used YouTube videos which encouraged speech and some signing (look up Miss Rachel to get an idea).
She's now way ahead of most of her peers in terms of speech. I'm sometimes still surprised with how she manages to communicate with us.
Just my n=1 experience.