When my DS was a toddler he went to a childminder / mini-nursery set up that had 9 toddler boys (by coincidence! It wasn't intentionally single sex!)
As several of the DC had younger siblings or ones on the way, the CM got each of the DC a baby doll and a buggy, and encouraged them to be caring towards their "baby" to help them to practice this, to help adjust to their new siblings.
Most days, they'd go to the park, each pushing their baby in a buggy, we got photos of this,it was so sweet, and well thought out by the CM. (She said it also helped them not run off and go in the same direction, bonus!)
I haven't read the article but will after DC in bed, thanks :)
"Gender neutral" toys are often seen as just the "boys toys". But, traditional "girls toys" have loads of educational value too (for all DC, obvs).