PANTS is an initiative from NSPCC to support parents, carers and educational settings to teach children about the importance of keeping themselves safe. PANTS helps children understand that their body belongs to them, and they should tell someone they trust if anything makes them feel upset or worried.
You can find additional resources to support you in talking to your about PANTS here:
https://www.nspcc.org.uk/keeping-children-safe/support-for-parents/pants-underwear-rule/