If we don't tolerate those, then we don't tolerate giving them the best alternative possible. Asking for more would make it uneconomical, and thus, economically destructive.
From there we get creative. We pay more to implement better working conditions, we provide aid to areas to send kids to school instead of to the factory, etc...
'Able' here is a complex thing; to look at just two countervailing parts, how little can employers get away with paying, but also how much can they afford to pay?
If the sweatshops do more than break even, then the employers can afford to pay more and have better conditions for their employees - but they won't if sweatshops as they are now are legal, common, and accepted. Most sweatshops do a lot better than breaking even, so if we got rid of them, a better alternative would be able to exist. (If you believe in General Equilibria, a better alternative would be forced to exist).
If so: Lat me tell you that 1) people are bad at evaluating their alternatives. Thats why we force our children to attend school as well, because our children might underestimate the long term positive effect school education might have for them, and 2) a child in a sweatshop might not have taken the decision to work for itself - it might rather work for the immediate benefit of their family, while taking the long term loss alone.
Well, if we're talking about giving away stuff, like freedom: How much could we help these people if we gave away, say 15% of the combined military budgets of the EU, Russia, China and the US?