I got 'lucky' when I divorced/ got custody. My daughter was 5 and her mother had been absent most of her life. I never bad mouthed her mother. I told my exw that "she'll make her own mind up about you." They have ZERO relationship,because my daughter indeed figured it out at about 12(she's 22 now). **I** think with kids under 12-13,who don't seem aware of what the exact problem is in the home, there should be a therapist involved in some fashion. Whether both parents meet with a therapist before telling the kids, or if you tell them in a therapy appointment about the split.. Just my $.02.