I used to work at a daycare and I had a lot of bilingual kids, especially English/Chinese and some of their parents were concerned that speaking Chinese would delay their English and I was always telling them no, the kids know there’s a difference and they rarely use words from one language while using the other. It’s amazing. Some of the toddlers couldn’t tell you that they spoke two, like if you asked them what’s this in Chinese they couldn’t but by the time they were four or five they knew they understood two separate languages. It was so amazing to see them just switch when they’re parents picked them up.