The best way for kids to learn English as a second language is to engage in a variety of authentic interactions with native English speakers their own age. These interactions can be centered around play, schoolwork or accomplishing other tasks that are relevant and meaningful to the learners.
There are many theories that attempt to explain the processes of both first and second language acquisition, but there is still no complete explanation for how these processes occur or how they can be accelerated. The one thing that has been identified as being effective at promoting the learning of any second language, including English is extensive interaction in the target language.
This interaction should take place in authentic contexts as part of efforts by the learner to satisfy real needs. In practical terms, if a young child who cannot speak English is put together with kids who speak only English, the non-English speaker is motivated and even forced to learn by the desire to join in the play, share toys and so forth.
Satisfying everyday needs, such as requirements for food, drink and comfort, can operate in the same manner. That is why placing a young learner with a host family that includes only English speakers is so effective.