If it is a union shoot, you will have certian requirements and limitations for the amount of work hours, payment, etc., but if it is a non-union production and you are just doing a random project that you want to cast a family member in, then go ahead and do it. You do not need to pull out any special stops for one cast member. You should at least get his or her parent's permission though. Many laws require paren't permission for using people under the age of 18 in a media production.
You can use the basic release form that you use for all other adult actors and just add an extra signature line at the bottom that says "Parent or Legal Guardian's Signature" where the actor is supposed to sign because of course, if the kid if 4 years old, you cannot make him or her sign the release form. It has to be an adult.
You also should change the wording in the release from so that Instead of saying things like "I give permission for my likeness to be used in this production", it says something more along the lines of "I give permission for my child's likeness to be in the production". The parent or guardian should also print their name in the release form as well.
For example, let's say that Charlie Sheen was still like 10 years of age and his father had to give you permission to use him in your production. In many cases, the release form would sound something like "I ___________(Martin Shee's name would be in the blank space) give permission for my child __________________(Charlie Sheen's name would go in this space) to be in the ovi production, etc. etc., and that should be all that you need as long as your release form covers all of the important and appropriate topics of interest to all parties involved.
