I wonder what has changed? People today who attempt to get a piece of land and do subsistence farming usually discover it is way more work then they are used to doing and quit.
They lack the 20 years of mentor led training to do all tasks related to farming and surviving that average medieval adults had. How fast you can do things when you are skilled compared to unskilled is massive, unskilled subsistence farming not being viable isn't strange.
Skilled or not, doing everything with hand tools is unending backbreaking labor.
Smaller families? Historically families were large and the entire extended family helped out, across all generations. In the modern age our families are smaller, and we consider it morally abject to have children work, with the elderly being expected to retire.