Is chronic constipation (daily miralax, (polyethylene glycol) frequent senna, glyc. Supp's aren't enough. Enemas needed often) in toddlers considered a Motility issue?

Stool retention. This is more an accident than a motility issue. When/if the kid decides one day not to poop, and the next day has a hard painful stool, they may try to stop having them. Over time stool retention causes physical changes in the large bowel causing poor emptying. Parents try short treatments that fail & the problem continues. This often requires a developmental ped or pedi GI working for a year .
Not likely. In a toddler who has otherwise normal development and muscle tone, it starts as a dietary problem with too little fluids, fiber, fruits and veggies and too much cheese, etc, that leads to constipation, then pain with passing stool, then stool holding, then enlargement of the rectal vault so it holds more stool before feeling full. Also, fear of toilets with potty training, or rewarding dry undies.