Kids under 7 cannot enter into contracts at all. Kids between 7 and 18 can enter into contracts, either if those contracts are entirely without duties to them (e.g. they can accept gifts) or if their contractual duties are somewhat negligible (e.g. they can buy sweets from their pocket money) or their guardians agreed to them being able to enter into such contracts. All other contracts are provisionally void (?!, "schwebend unwirksam"), i.e. can become void as soon as their guardians disagree with the contract or can become fully valid once their guardians agree.