So many implying it's women's working full time that is the cause of it, masking it as "parents having to work". Think of extremely successful countries and cultures where the concept of stay at home mothers is almost non existent yet childhood is wholesome and people grow into intelligent capable individuals and these countries have very high standards of living e.g many Scandinavian and other European countries.
And if you are old enough to remember quite a few women staying at home during early childhood in a short period in history (60s-70s), since less affluent women always had to work, you will remember that motherhood was a lot less intense with children spending almost the whole day outdoors, no overscheduled activities,and siblings having responsibilities.
And nursery. Implying nursery is to blame??? Kids who go to full time nursery are far more advanced on average.
What it will be is the lack of outdoor free play, overscheduled routines with 2 and 3 year old being driven to dance and football classes when they should be playing, and then sitting in front of screens all day, parents' belief in advancing their kids through these activities until the child loses all ability to play freely, and, more importantly, screens and gaming that destroy any ability of children to play independently. Plus cars and being driven everywhere. Too many cars and population being more transient in big cities are prohibitive to having free spaces for kids to play out independently.
So by age 5 or 6 you end up with a child who's done it all, is bored out of their mind, and has "outgrown" actual physical and imaginative toys and games while being unable to toilet themselves or climb the stairs.