The single parents of toddlers working multiple jobs either pay for childcare or have whole network of familly members to help them. There is no way around the fact that toddler needs supervision incompatible with most of work.

Also, most grandparents in fact are in working age when the grandkids are small. Some are sick, some never returned to work after kids grew, but quote a few always worked or returned to work. And even with those who are at home, asking them for daily babysitting of 4 kids is quite a lot.