Not op/parent, but I too have ADD/ADHD-PI and is helped by what some call meditation. My physical therapist at the psychiatric unit mostly saw them as an excercise which have appeared to help people like me.
Briefly, or maybe not so, what was taught to me was an excercise to sit down and experience myself emotionally and physically, with a focus on the latter, and without judging or interpretation.
Thoughs may come and go, I don't cling to them, but neither do I force them away.
There is a physical part in an intention, a will to let the body find a posture that feels both solid and effortless where the respiration movement is not isolated to a small part of the chest or abdomen. The breathing is hard to describe, but when it works right it barely feels like I'm breathing at all, as although most of the chest, back, and abdomen is somewhat involved - breathing becomes so smooth and effortless compared to what my otherwise tense body usually do to breathe.
Immediate effects for me is that the world feels more real, solid, and even that the floor feels softer.
Sometimes I think that maybe this is what feeling both relaxed and alert means? Neither is something I think I have felt more than very rarely.
Otherwise, regulating emotions, tuning out noisy environments etc is long term effects.
To me the excercise appears to reinforce the importance of body perception, raw unprocessed emotions, and physical stimuli over internally generated feelings and thoughts. A stillness to listen to even when I'm not doing the exercises, a recliner in my mind to lean back into when there is too much chaos around me. Not to flee, but to hear and see without getting overwhelmed.
As ADD is characterised by a mind constantly jumping from thought to thought, one that is never still, it's conceivable that some kind of balance between various parts of the brain gets upset, somewhat like when everything becomes a nail because all you have is a hammer.