Talk to your child. Even if your son displays exceptional musical abilities and you are certain he could make it big at Disney, this doesn't mean you should set him up with an audition before first consulting your child. Talk to him about how he feels about auditioning for a broader audience on television. Ask if this is something he would like to try, rather than forcing him into it.
Don't limit your child. Your child may be musically talented, but if the only current open auditions available at the Disney Channel are for acting roles, let her audition for what is available. Even though it might not be exactly what you and your child had in mind, never limit your opportunities. If there are casting calls for child actors, give it a try. Remember, one open door could lead to even broader opportunities including singing.
Know where to look. Many auditions are advertised quietly, such as through newspapers or websites. One place to begin would be the Disney Channel website or audition websites such as disney-channel-auditions.com, where you can browse through available auditions and casting calls for Disney in selected areas.
Be encouraging. Do not scold your child or express deep disappointment if he is not selected for the role for which he auditioned. Openly display confidence in your child's ability, and encourage him to not give up, even if he has received several rejections. The more encouraging you are to your child, the more confident he will be with his own ability, which will shine through the next time there is an audition.