The "be going to" meaning in this form of simple future in English doesn't exist in Greek. The suggested form "Πρόκειται να" is just one of the possible translations, not a general rule. "Θα" could also be used interchangeably.
I'm curious why my answer wasn't accepted: Εγώ πρόκειται να βοηθήσω το παιδί Is it incorrect to use a pronoun with πρόκειται?
No, it's not. Added!