Also relevant is FRE rule 404.
http://www.law.cornell.edu/rules/fre/rule_404
The notes specifically mention this exact type circumstance:The amendment makes clear that the accused cannot attack the alleged victim's character and yet remain shielded from the disclosure of equally relevant evidence concerning the same character trait of the accused. For example, in a murder case with a claim of self-defense, the accused, to bolster this defense, might offer evidence of the alleged victim's violent disposition. If the government has evidence that the accused has a violent character, but is not allowed to offer this evidence as part of its rebuttal, the jury has only part of the information it needs for an informed assessment of the probabilities as to who was the initial aggressor.
Thank you.
And this.
(2) After a child has been adjudicated delinquent pursuant to subdivision (3) of subsection 1 of section 211.031, for an offense which would be a felony if committed by an adult, the records of the dispositional hearing and proceedings related thereto shall be open to the public to the same extent that records of criminal proceedings are open to the public. However, the social summaries, investigations or updates in the nature of presentence investigations, and status reports submitted to the court by any treating agency or individual after the dispositional order is entered shall be kept confidential and shall be opened to inspection only by order of the judge of the juvenile court;
http://www.moga.mo.gov/statutes/c200-299/2110000321.htm