No! However, minors under the age of 18 must be accompanied by an adult, so you will need to purchase a spot for both the adult AND the minor. Remember to allow for this as you make your plans to visit the set or to be an extra.
Please be aware that babies or young toddlers/children may be asked to leave the set if noise is an issue.
Here's an article about adding guests to your PIF: Here
If you're coming to be an extra, both the adult(s) and the minor(s) will need to be in full costume.