My son, to everybody’s surprise, learned my(father) native language (Hungarian) much better than his mother’s native language (Ukrainian), even though we both are the only ones talking to him exclusively on our language, as we live in an English speaking country. He speaks Ukrainian ok, but his Hungarian is just perfect, and is at par with English. It was interesting, and I didn’t know what to attribute it to. Then we got another kid, and as he is approaching 18 months now I can see already he speaks way more Hungarian words also! Indeed, my anecdotal conclusion was that it must be the language (and mind you, the Ukrainian and Hungarian languages are absolutely different) that made the difference, everything else seemed the same, especially with WFH for the past 2 years.