ParentKit is free to try for 1 month. No credit card is required to sign up. You can upgrade to either a 6 month or a 12 month subscription right from inside the App on your iPhone.There is no automatic payment, you decide if you want to subscribe or not. Your one month free trial starts as soon you create an account.
There is no limit to the number of profiles or devices that you can have. All of your children and their devices are included in one subscription.