I just wanted to add - for next time,

After your discussion with mom offer to have her help in another area of the show (tech. or something).  Tell her that you would like to see how she works and if you think she has the drive and proffesionalism perhaps she will be cast next time.  I often do this and if the kid or mom says no then I realize that perhaps they don't have the heart to be involved anyway.  And I will tell them that - that if they truly have the love for theatre they will start out small and work their way up - if not I don't want to work with them anyway.

My condolences.  Have you ever thought about putting on the audition form?  I imagine minor's must have parental permission to even try out.  I have a standard line in REALLY BIG LETTERS--The director is the final authority in all casting decisions.  The director will be more than happy to discuss your particular audition, but you will not be allowed to re-audition, and the casting will not be changed.

This has prevented a lot of the "Why didn't my child get the role of ___________?  She's much better than __________."

I've been reading these posts and had to add my 2 cents;  I have been directing children and casting them for several years and at first my husband and i have had many problems such as this.  then we switched our audition system.  They are closed.  a child can come in and do a song they know and recite a nursery rhyme or whatever and their parents can be in attendance and that's it.  When it comes time for Callbacks we even tell parents these are closed to parents and we tell them why . . that we feel a child will ultimately give us more if their parents are not watching and do tell them that parents have been an issue in the past.  We make no bones about it.  Nothing is worse than making a casting call and having a parent tell you that their child did better than so and so . . .the children handle it better than the parents sometimes!!  Since we've had closed auditions the instances of these calls have decreased significantly!  so much so that another director decided that open auditions 2 years ago would be fine . . . wouldn't you just know it...those venomous parents popped up again! 

As well, though, when we make our calls and we're calling kids who didn't get cast we always try to do 2 things:  start with the postives, so when we go through the casting we write on every audition form something positive about that person and then we write down one of the major things that contributed to their not getting cast:  lack of projection, enunciation, stage presence, singing was not strong, etc.  The parents generally take this well are glad that we have something for their child to work on.  Sometimes it is not so easy and it's merely a toss up as to who we cast: don't know the children; talent is equal; look for the part is equal and we just go with our gut and we try to be truthful with these children and tell them that there were a lot of kids who tried out and this is the way it fell.  Most kids and parents receive that one ok, as well.  we try not to sugar coat anything nor do we try to be too harsh.  and we always encourage them to come back. 

Parents like this make me not want to work with their children...unfortunate as that is.

An excellent point.  It's important to let all of your auditioners know what you are looking for, what you will expect of them if cast, and what they should expect from you.  Be clear, be thorough, and be true to your word.  There are probably as many inept directors as intolerable stage-parents.