These are the intervention models I'd consider that will help you with a family-based, attachment-focused approach - both because they are sound trauma-informed, attachment-focused therapy, but they also have materials and strategies available for parents to implement. Some have already been mentioned: DDP/PACE, TBRI, Circle of Security, the ARC Model, Theraplay, Sanctuary Model, the Nurtured Heart Approach. Being versed in more than one of these is always a good idea. In my experience, children and families need different "tools" at different stages - and while these models are GREAT - each of them have their strengths and weaknesses - and each adds tools to the overall toolbox.