Carrie Morrow arranged a gay-friendly workshop at the school to teach children about diversity.
The theatre company which ran the workshop performed a fairytale in which two princes fall in love.
But a “small minority” of parents took to Facebook to lambast the decision.
One father expressed his annoyance when his son came home “talking about gays, saying he had learned about gays.”
Local media reports say two men have been spoken to by police officers after posting comments on Facebook.
Carrie Morrow, who has worked at Sacred Heart RC Primary in Atherton, near Wigan, for 13 years, refused to back down after the criticism.
She said: “We are very proud of what we have done, express.co.uk reports.