Referring to famous Morrissey's "Children in pieces" b-side.
"To be in pieces" means to be shattered or broken. On an emotional level, you can say "I'm in pieces after she dumped me"
Quite similar to it's literal sense, imagine a glass bowl in pieces i.e. it's been smashed on the floor.
The lyrics from Morrissey's song go
which is a reference to the large scale abuse that took place in those schools and thus their childhoods have been damaged.