Healthcare benefits came about in WW2 because Roosevelt instituted a wage freeze. Companies could not offer higher wages to get the best workers, so they found a workaround by offering health care benefits. It turned out to be a big win for workers because the cost of those benefits was pre-tax, rather than post-tax. So it stuck.
Children are not freely consenting adults, which is why they get special legal protection. That's irrelevant to what we're discussing here.