hi, my son has just got his Green Card for the USA, and is living with his wife in Los Angeles.

He has savings in a UK savings account and want to move it to the USA.

I understand the exchange rate and transfer fee implications, but what is the US law?

1/ Is there a limit to what you can move to US account?
2/ Does the US require proof of where it came from in the UK

3/ Is it better to move it to our account and make it look like a one off gift?

Any guidance would be appreciated, as there seems to be be a few different opinions!