You are free to choose in which way they want to perform this activity with your children.
It can be the planning of an event using a planner template, it can be the creation of one of the elements of the party, for example, the creation of invitation cards or of decorations, it can be the actual inviting process (calling on the phone, sending email..), or it can the actual execution of the party.
What is important is that the children, together with you, the parent, are part of the organisation process and the reflection that entails inviting people over. It is also important that you highlight the problems or challenges that might arise during this activity (such as doubts as to where to hold the celebration, or the particular diet of one of the guest), and guide the children through finding a solution. It is very important that the final decision is made by the children as it is about offering them situations in which they can make mistakes without any serious consequence.