He will need to disclose it. Depending on the reason why he was deported (was she simply illegal or was some crime? you did not say), there might be a waiver (I-212 possible. You need to pay for ONE petition I-129F ($340) listing your finance. His children must also be listed on the form where appropriate. At the consulate, there will be 4 applicants (Fiance + 3 kids), so you will pay 4 times $350 for the K-1 and K-2s visas. Good luck.
Answered on Mar 16th, 2011 at 12:33 PM