I grew up bilingual. Now that I come to think of it, more like multi-lingual. Back in the day, it was thought that a child's fluency in more than one language would "confuse" her brain, and parents, like my mother, were told to shield their children from other languages until they were adolescents (or forever, whichever came first).

My mother, as was typical of her, let me learn whatever I was going to learn. So I grew from babyhood speaking Swedish (from my great-grand and grandparents) and English. Then, as I went to nursery school (a WWII cooperative nursery), speaking French as fluently as English.

As you have no doubt surmised, learning other languages did not impede my command of English; in fact, I think it improved my mental agility and speed.

Having more than one language already at my command in childhood (we can add the language of music) meant that learning yet more languages was relatively easy. A generalized facility for language learning seems to be implanted in my learning module, so computer languages, Italian, Hindi, Kannada, Ilocano, ASL, street English, were all grist for the mill. It's easier to acquire additional languages for me than if I had had only one mother tongue.

I was able to master mathematics when I realized it was once again another language.

The downside is that I occasionally "block" for a particular word, or a word (or phrase) will come out in another language, particularly when it is one better suited to the occasion than the primary language being spoken in the current conversation. Or sometimes I will not be able to say the word that I was just thinking of, when it was just on the tip of my tongue, and finally I'll end up saying it in a different language.

Maybe it's just that there are too many words/phrases to choose from. I don't worry about it, since my monolingual friends seem to suffer from the same phenomenon, just a little less often.

Thank goodness for synonyms!