Y'know, come to think of it, sometimes, kids are the source of
arguments amongst couples. Maybe the husband doesn't like the way
the wife treats the kids and vice versa, they disagree and start to
argue and then both end up fuming mad at each other. Day in, day
out, they see the same thing persist, they can't stand it, but they
can't do anything about it to change the other party, so the anger
festers...
I guess it depends on how headstrong the husband and wife are.
Besides, sometimes both want the 'best' for their kids but they
just don't agree on what 'the best' is. 
Maybe the husband wants the kid to experience a carefree,
adventurous life and wants to let the kid run around and play
freely but the wife wants to keep the kid safe and protected...
Y'know, stuff like that can tear a couple further and further away
from each other until finally, what you get is an empty shell of a
marriage, where both parties have learnt to put up with each other,
and things aren't so bad to warrant a divorce, but yet things can
never be lovey-dovey again cause both have a little resentment
towards each other.
There... an alternative viewpoint that, IMO, is very realistic.
