i don't know if it's possible for every child .... maybe I didn't handle it at best .... I will never know
but one of my children couldn't process 2 languages at the same time
that was between the age of 4 and a half and 7 and a half
when we moved each time
he would refuse to speak the language of the new country for quite a few months
but then when he would, he would stop speaking the previous language
i don't know if it is his brain who couldn't process things as his older sibling could
or if he just was lazy ou just wanted to take it easy and not make the effort
...there were times when I tried & he would tell me that what I was asking was difficult ....
so I got the impression that is just wasn't "physically" possible for him
I must say that the timing of our first move was job motivated
and in restrospect not the best time for him because we had just noticed/been told that he had a slight language delay in his mother tongue
(so we had at wait a good year in the new country, for him to start speaking the new language, before he could be refered for speech therapy in the new language ..)
and on our return 3 years later he had totally forgotten his mother tongue
AND had to have speech therapy for about 6 months, in particular one of the sounds (which he could do perfectly well before our first move)
he just couldn't remember how to utter it native like ...
(= he was speaking his "former" mother tongue with a foreign accent )
of course he stopped speaking his second language within 6 months again
(which we are working on now, more scholarly since he's older,
I'm using some of these workbooks one can buy everywhere)
and it took us a little while, like a good 6 months after I let him concentrate on his first language for about a year
but he has a reasonnalby passive understanding of his second language (which he speaks with an accent now, accent he didn't have when in the country)
just to say that for most children it must be possible to get them to pick up several languages from their environement
but for some children that task is more challenging, individual differences and all that ....
(+ maybe too much suceptibility ???? I know I get really annoyed when my MIL , who cannot speak a foreign language, tells me that I should speak
this or that language depending on what she wants such and such person in my surroundings to learn this or that language ....
maybe my son takes after me on that department and will resist other people trying to make choices from him ?????)