It's a typo.
"After school" is a prepositional phrase in the middle of the sentence. These phrases do NOT take commas. Generally, you only use commas to set off prepositional phrases when the prepositional phrase is used at the beginning of a sentence (and then it is customary to do so in those circumstances where the prepositional phrase is long or not using the comma would cause confusion).
I suspect that the sentence may have originally been written "After school, may I play, Mother?" This sentense is a tad awkward, but the comma usage would raise no eyebrows. The editor or author, realizing that the sentence could use a bit of word placement modification, made the swap; the commas were left behind like little breadcrumbs.
Yes, I taught writing back in the day.

I highly recommend
The Deluxe Transitive Vampire. A quick readthrough usually sets me back on the straight and narrow when I've become lax in my usage.