Total double-edged sword, because they'd lose costumers.
Then again, when we're talking about fancy restaurants and first-class air flights, very few young couples could afford it anyway, so probably they won't lose any money.
When referring to more public places, banning babies / toddlers would be a huge mistake. Young couples like to spend time in coffee houses and other "adult places" as well, and leaving the kids with a babysitter is not the best solution.
A better solution is for malls and such which provide the kids entertainment while the parents can relax not too-far away.