Can I put the other side of the argument without everyone jumping down my throat.
It's a long time since I had to use childcare but when I did:
-It was a lot of money. You don't earn the sort of money that pays for a nanny by doing a 9-to-5 job. You had to have responsibility or commute or, basically, have (for want of a better word) an 'inconvenient' job that sometimes involves having to stop on to sort a problem or getting caught in traffic. The sort of job that makes it more likely that you will be late home.
-The chances are that, at the stage where you have young children, you are still trying to climb up the career ladder, still having to impress people and make your mark. It is one of those ironies of life that I now have the authority to say "clear my diary, I'm having the afternoon off for a nativity play", now that I no longer need to.
Back in the day, I wouldn't have dared to be so bold because it could have impacted on promotion.
What I'm trying to say is that employers aren't always in control of their day. They don't want to be home late any more than nannies do!