b2 visa

[narf1020]

I have a 10 year old boy living with us here in the u.s.a. attending school. He is a canandian citizen and has been living here approx. -7- months. On his passport visa stamp it only shows the date he entered the u.s.a. it does not show any expiration date. Also - he does not have a I-94 form. My question - how long can he stay here?? What can I do to make sure he is legal. We are not his parents.

THANKS for any help.