"Income shock"
If you are stupid enough to start having children before you can figure out whether you can afford them, then too bad. It's your problem. You figure it out.
I can see how this would turn out. Sure, the parent (s) will appear to be paying for these kids by sacrificing part of their SS. But then it will turn out that there won't be enough money from their own SS, so the contributions made by people like me who didn't have any children or those who saved to afford their kids will once again be stolen to pay for the stupid, lazy and irresponsible who didn't plan for their own kids.
This scheme doesn't modernize SS. Modernization would be privatizing SS or maybe giving workers their contributions in a lump sum when they retire and telling them to invest it . No, this is just going to be another for of welfare.