As a therapist I have used a few of the mainstream DBT books that help clients individually and in a group setting and while they are good, I would like for you consider the following workbook as a great addition for your DBT toolbox.
Carol Lozier is a wonderful DBT writer and social worker who has been doing this for 30+ years and has written other books on DBT and helping those to understand the skills.
I was gifted this book during the COVID-19 Pandemic and while writing my own workbook. This workbook is so wonderful for children who are in an age group that I am not trained in ( under 14 ) and she does such a great job with her examples on mindfulness and how she describes these abstract ideas/concepts to a younger population. She has some wonderful activities for the parent/caregiver or therapist to use with the client. I have not seen a workbook for this age range that truly tackles all of the DBT skills.