If you want to leave something to a person under 18, you will be asked to name people you trust to manage what you leave them until they reach 18 (or another age that you can choose).
If you’re worried how they will manage what you leave them after that age, for example if they have a disability or long-term condition, you can ask the people you trust to manage it on their behalf on an ongoing basis.
You can tell them what you would like the person to get, and in which circumstances, and they agree to act in that person’s best interests.