From Crisis Aid International:
Tip: Consider limiting use of all Internet capable electronic devices to common areas of your home where parental supervision is consistent.
Tip: When talking with your young children about Internet dangers, explain: text, photos and videos should NEVER involve no clothing or only underclothing.
Tip: If you believe your child is being targeted online, do NOT confront the person or close account or app. Take a photo WITH A DIFFERENT DEVICE and document the username/time stamp (do NOT screenshot it) and contact law enforcement right away.