I am going to explore the impact of Adverse Childhood Experiences and Childhood Attachment styles on behaviour of adolescents after the development of these scales. On which population (Adolescents or Children) i should validate these scales?
I would be skeptical of using any self-report measure on children if they are in a younger age bracket (until approx 9-10 years of age) because they lack the cognitive capacity to engage with the instrument in a self-reflective manner. Even adults from clinical populations may lack that capacity so I'm really not sure about the quality of information one gets from administering self-reports to younger children.
A dyadic study will be necessary where caregivers and the adolescents will be your participants. The caregiver in retrospect, will supply information on what happened when the adolescent was a child, and of course, you get effects of childhood experiences directly from the adolescent. The alternative is a longitudinal study, where you observe the negative experiences and attachment styles in children, and then follow them up till adolescents to measure the effects.