OK, then he is definitely taking the piss.
He appears to have a total lack of appreciation between what it's like having a leisurly afternoon to oneself, childfree with no housework, vs. being home on a day with a kid with a cold and the house a mess.
You need to re-dress his understanding.
Unfortunately the only way I've seen that to work is if you get a part time job and force him to deal with the reality - because talking until you're blue in the face isn't much help. And if you're not strong enough, you'll end up like a friend of mine who works fulltime, just like her DH, in an office, just like her DH, the same hours - and yet she does all the housework too.
Needless to say, this is the same friend of mine who got divorced last year - I remember her talking about the "lightbulb" moment when her DH was away from home for a conference thing for just over a week, and she felt like life was easier without him there... no one to have to pick up after, no changing schedules at the last minute, no having to keep him happy or whines/arguments if something wasn't done his way, no one to say they'll hang the washing out but then it doesn't get done, etc... she's like a different person now. Much lighter and less stressed. That's a terrible thing, I think -to see how much happier she is when she only has her real DCs to deal with! Being part of a relationship is meant to make each party happier, more fulfilled, working together, stable - if that isn't happening, it's sad but sometimes easier to go it alone.
I'm not suggesting that you get divorced, my wider point is that your DH's lack of appreciation for what you're doing day in day out needs addressing. A sharp reality check etc.
Getting his mum to look after DCs whilst his wife is away on a rare occasion? WTF? 
He's pretty much a weekend father, from the sound of it.
Participates in all the "fun" stuff (going to the park, family time on Satudays) but not a good dad when it comes to cleaning up the shit off the changing table or taking turns to check on an ill child. Poor show really.