Is COVID really to blame for developmentally delayed kids, still in nappies etc?

It seems to be an increasing trend of Millenial and Gen Z's kids where anyone born in the last 5-7 years seems to be developmentally behind in ways that are just outright bad. Kids going to school in nappies and pushchairs, kids without any core strength, dexterity or reading comprehension.

Is COVID really to blame here? I imagine it didn't help but that's no excuse not to toilet train a child. Is bad parenting black and white the issue here? Do you think there are other factors at play.