I-94 expired for H4 minor - will a visit to Mexico work?

[marc_ely]

Hi
I am working on an H1B visa. My visa, passport and I-94 are all good.

My firm has just started green card proceedings for me and spotted that my 11yr old sons I-94 expired 90 days ago (in May).
He has a H4 visa and a new passport.

I know he has to get a new I-94 as soon as we can.

Will a visit to Mexico work for this? i.e. over the border, queue up for I-94 and come back.

Is his visa still valid if his I-94 has expired? If it's not valid he wouldn't be allowed back in. Would they really do that for an 11yr old if his fathers visa was in order?

Thanks