You just need one account per family. However, each of your family members will have their own log in, including your kids. When you invite other adults to Stridepost, they will be sent an e-mail to join your family and register for Stridepost. Once they're in, they'll automatically be connected to your family!
When you add a child to Stridepost, there's no need for them to confirm their e-mail. Simply have them log into the Stridepost app from their smartphone or tablet using their username and password you set up.