NOT a trans thread! 
My DD is almost 6 and doesn't use the correct pronouns for people. She isn't consistent, she knows 'she' and 'her' go together and and 'him' and 'he' go together, but she can't always apply it to the correct sex. For example she'll call a male friend she/her for a few days (I always correct her) and then he'll be him/he for a while, and then she'll go back. She has never really grasped it, and does this with everyone in her life.
Is it normal for a child her age to get pronouns mixed up? How old were your children when they nailed it?