Abraham's children

In the 15th-c. English mystery play known as The Brome Play of Abraham and Isaac Isaac comforts Abraham before he sacrifices him saying "Ye have other children, one or two". That surprised me because at this point in the story Abraham and Ishmael are (presumably) not on speaking terms and Sarah is still alive, so Abraham is not married to Keturah yet. Also much of the emotional impact of the story was, in my view, based on the fact that Abraham was ordered to kill his (effectively) only son.

Does the medieval author by giving Abraham "other children"

1. mean Ishmael
2. refer to some apocryphal tradition in which Isaac has siblings living with him
3. or is just confused?