Well mostly what businesses hate is the lack of planning and having to fork out cash which is associated with family friendly policies.
So what you'd want to achieve is for both the employee and the company to get a mutually beneficial arrangement. So the employee gets flexibility, the ability to return to their job, and rearrange hours etc to suit. But the company doesn't have up-in-the-air arrangements which cause resentment amongst other staff.
So firstly EVERYONE should be entitled to petition for flexible working and prove how it would work to the company's benefit or at least not to its detriment. The business should still be able to refuse on the grounds of it being detrimental to the business.
Secondly leave should be available to everyone, but the arrangements for covering the workload should fall to the employee and if the arrangements don't work and the company has to step in to rearrange stuff or re-hire a temp, then the job shouldn't have to be kept open for the employee's return. I actually think this is fair to everyone and makes it in the employee's interest to do a proper handover and actually care about what happens in their time off. Likewise if other people end up covering your workload on your days off, then the flexible working arrangement should be able to be changed.
Thirdly, "mummy hours" or holidays should be fairly allocated - so whether that's everyone having to work either before Xmas or before New Year's, or perhaps if you want a day at home you need to take that Wednesdays instead of Mon/Fri. Whatever policy is in place, it should be clearly communicated.
I actually think a lot of the problems with mums at work are caused by them being entitled to these benefits without having any of the responsibilities or administering them. It's a complete headache for the manager who has 5 mums in her team ALL wanting Fridays off or all wanting Summer holidays on school holidays.
Likewise finding cover for maternity leave is always difficult because you can't entice someone with current skills and experience away from a permanent job for only a short contract. It's made even more difficult because the way the leave arrangements are at the moment make it in the mum's interests not to be honest about whether or not she returns to work. If they had to make all the arrangements, do the handover and find someone suitable, they would be pretty certain about coming back to work. Otherwise they'd just quit and avoid the hassle, thus freeing up a new permanent job.
Mostly though if we want to support families then we need to pay people a decent wage in the first place - so that one person can afford to stay home. The UK has a really high cost of living and low salaries compared to other places. I'm convinced if we cut a lot of the red tape of employment law, then we could afford to pay employees more.