I'm not actually sure where they plucked the 'quarter' figure from because unless it's hidden somewhere else the article actually says that '90% of teachers said they had atleast one student in their class who wasn't toilet trained'.
That's a big jump from one in every four kids.
As for the rest of the article, I think it's incredibly easy to blame parents, and whilst I'm certain lazy parenting is a factor here, I think we also need to step back and look at the world right now.
COVID caused mayhem for many new parents; my child alone basically didn't socialise between the ages of 18 months and 3 years. And at that age, kids being around other kids is absolutely essential for their development.
Parents are also working longer hours than ever, and money is tighter than it's ever been. Whilst these don't get parents off the hook, the idea that the blame lays entirely on parents is a touch shortsighted.
Access to affordable and accessible childcare would go an awful long way to alleviating some of these issues, but again, there's no silver bullet and no one group is responsible for all of this. Parents need to be better for sure, but society does a terrible job of setting them up for success.