Thank you for your contribution Jasper!
I don't think that adding the penalty box would require much modification into the rules, it would mainly implies changes for:
- Field specification
- Goalie specific rules
- Penalty rule / Indirect free kick in penalty area
I agree that it would make sense to reduce the height of the goal for KidSize, currently the main reason to have the same size is to keep all goals with the same specification. If we distinguish the goals, it would also make sense to reduce the width of the KidSize goal which is currently almost half of the field width.
For the adult-size, it will be mandatory to increase the height of the goal because we have decided to increase the maximal height for adult-size robots next year. However, I don't think it is adviced to have thicker posts, because 12 cm is the current limit for full size fields in human soccer.