Camping is a great activity for families! At this time, it is up to each individual Host to determine if kids are allowed on their property and to determine what age kids need to be included in the booking headcount. The majority of Hipcamps allow kids and some Hosts do have rules where kids under a certain age are free, but these are policies that are entirely up to our Hosts.
Many Hosts share this information in their site description, but if you aren't sure if kids are allowed or if kids under a certain age can come along for free, it's always best to contact the Host first.