We learnt to always work as a team and never let the child divide and rule.
The other invaluable fact we discovered is that a child has simple needs. If they feel loved and secure, with a structure of rules and routine around them, a happy child is the result.
A child's job is to push the boundaries and it is the parent's job to maintain the boundaries, but the art of parenting is knowing when to slowly release the boundaries to allow them to grow into adults.