Could a Space Marine father a child? I haven't been able to find any canonical answer either way... I've found hints that it may be possible, but a lot of people seem convinced it's not.
We just don't know
This is never directly addressed by Games Workshop or the Black Library.
Space Marines probably could, but loyalist marines almost defintley wouldn't.
They (probably) can't reproduce with humans
Space Marine DNA is just too different to normal human DNA, so there is no chance to reproduce the natural way with human woman.
Regarding sex - Marines CAN have sex and almost all of them are simply beyond that need - I remember in one book marine was taking regular showers with female warrior and completely couldn't understand her advances (he later mentions that he was simply conditioned to not feel desire), but was still finding her attractive "like you find dangerous animal or weapon attractive". The only loyalist marines that DO have occasional boink are Space Wolves, who drunk with their mead sometimes take Fenrisian women (because women form any other world would be too fragile).
Regarding Chaos Sp ace Marines - yes, Slaneeshi do enjoy sex (and thousands other pleasures), but again the purpose of it is not reproduction.