When we had dd I did 100% of the childcare, including evenings and weekends. As a newborn she had horrendous colic and would scream from 6pm until 1/2am every night and would then wake hourly for feeds. I only remember dh taking over once and that was when I put her on the bed and left the room (I was going to the toilet but he didn't know that and thought I was leaving her indefinitely).
It didn't really occur to me that the working parent would share the nights until other people were outraged that I did it all (dd has always been a terrible sleeper).
Since ds has been born dh has had to help me at night. I go to bed shortly after the babies do so I can get a couple of hours sleep before ds wakes for his first feed. I then feed him/change him/wind him etc, if he settles easily great, if not I pass him over to dh (who is usually still up anyway)and he settles him for me. It does mean that dh sometimes gets to bed an hour or so later than he would like though.
When ds wakes after that (only 6 weeks old so still on frequent feeds) I'll do as above but settle him myself. Some nights this means I'll be up from 1-3am with him and then again at 4. DH very occasionally will settle ds at one of these times but only if I tell him I physically can't get out of bed(bearing in mind i'll have already been up wih ds for an hour or so by then)
He complained a few times but has done it willingly since I pointed out that after a few nights of only 2 or 3 hours sleep not even in one stretch he really shouldn't consider me fit to look after his children!
Now that he also helps out at weekends he realises that it is hard work looking after a toddler and a newborn (particularly a very unsettled newborn who likes to be held all day) and is more willing to share the nights. Once ds starts settling more easily and/or waking less then I won't expect dh to help on weeknights anymore but I hope he still will at weekends.
DH also gets the lie in both weekend days, mainly because once I am up and know it is day I find it impossible to go back to sleep!