I’m afraid it may need to wait til they’re a bit older, but check out the Tiffany Aching series by Terry Pratchett.
The premise is fairly simple – a young girl in a fantasy world decides that she doesn’t want just live on her dad’s farm making very good cheese – she asks too many questions of her teachers and isn’t like the princesses in the books – so she decides she wants to be a witch instead.
First, she takes out a pond monster with a cast iron frying pan (who was going to eat her little brother) – then she goes to investigate exactly what kind of pond monster it was and out why it was in her world, and tries to find it again using her brother as bait. Eventually, she defends her steading, claims what is hers and realises that witching is her in lineage.
Pratchett’s entire collection is worth reading, but the witches hold a special place in my heart.