What a heartbreaking situation to be in bjane.
If the OP's son were to turn up in 2 or 3 years time trisher he would have to take full responsibility for any decisions taken about his children, whether he's a part of that decision making process or not.
He has abandoned his children and having not seen them for 1.5 years is very close to losing his parental rights, and rightly so IMO.
I've got another 'keen'... Ouch!