I shouldn't do this to myself but I regularly browse the guinea-pigs on Gumtree 
I've noticed now alongside "Kids allergy" / "Kids lost interest"/ "Work commitments"/ "Moving House" there's a new one...........
"My kids have outgrown them"
Outgrown like a pair of old shoes. Cast aside like a pair of smelly old plimsils at the end of the school year 