Legal Question in Juvenile Dependency in Michigan

Is it "illegal" for the 10 and 12 yr olds to have sex? Technically, yes ... because no one under age 16 has the legal power to "consent" to sexual activity. I have heard of a very few prosecutor offices who would charge both parties under your facts with juvenile delinquency petitions for criminal sexual conduct ... but that is very, very rare. Most prosecutors would not charge here because the children are still "voluntary" having sex, and the legal consequences from a juvenile CSC prosecution (including sex offender registration) outweighs the public's interest in intervening.

Is it "illegal" for the legal mother to know about her children having incestual sex and doing nothing about it? Not "criminal illegal". But it could be seen as "parental neglect" that could get Children's Protective Services involved, and a civil neglect petition being filed in the Family Court. At this point the issues would focus on "what did the parents know & when did they know it & what did they do after they knew it?" There are usually conflicting facts on those questions.

If you are concerned enough to post this question here, why not call your county's Michigan Department of Human Services office and talk to a CPS worker? As a "reporting party", your identity is kept confidential under law (in fact, it is a misdemeanor for someone to disclose that RP's name). You can also talk to your county's prosecuting attorney's office regarding how they might handle such a set of facts (although they may want a police investigation to determine what the 'facts' really are).