I'm not sure that there is a rule about the age to have the "sex talk." If you feel that your child is of an appropriate age and maturity level and you are her parent, then, in my opinion, it is perfectly appropriate to have had the "talk." As far as CPS, if they do get called to investigate, chances are, they will talk to you about what was said and talk to your daughter. If it truly is how you have represented, I personally do not believe you have anything to worry about. As a parent of a similar aged child, I too have had the discussion with my child - I don't anticipate CPS taking my child away.
I agree with Ms. Rosenblum. My only concern is that Nevada's legal age at which children are deemed to be able to consent to sex is 16. The argument could be raised that by giving her condoms at this age you are encouraging her to engage in underage sex. That might not look good if there are other facts that her mother could use to make it look like that's your goal. In my personal view, the "sex chat" is absolutely appropriate at this age, but providing the means (and implicit approval) to engage in sexual activity at 12 is problematic.
You gave condoms to a 12 year old? In my opinion, you just gave her permission to engage in sexual intercourse, which is illegal at her age. As such, your actions could be deemed criminal in contributing to the delinquency of a minor. Having the sex talk is fine, but what made you decide that was your job and not the custodial parent's job? What made you believe it was okay to have the talk without discussing it with the custodial parent first? I'm not sure CPS will do much, but the custodial parent may have grounds to limit your contact with this child and perhaps to ensure that your contact is supervised. If you would give her condoms, it isn't much of a stretch to believe you would allow her unsupervised contact with boys and/or even encourage sleepovers with the opposite sex. The custodial parent has every reason to seriously question your parenting judgment under these circumstances, and to take those actions necessary to protect the child.
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Under the facts you have presented, I don't see enough for CPS to take action against you. However the custodial parent may be able to take actions against you in family court and limit the contact between you and the child. However, this will greatly depends on the facts. If your 12 year old has physically developed early and has somehow indicated that she may engage in sexual intercourse, then you may be justified to give her condoms but not before you talk to the custodial parent about it.