S.H.
Potty training is in stages:
1) peeing in toilet
2) pooping in toilet
3) Night time dryness.... which can take even until 7 years old to attain. Normal.
Pooping in a toilet... is often the 2nd part of potty training and it takes time. Don't push it... or the child will start to get Constipated and "withhold" their poop. Then it hurts, and the poop gets harder and harder, and then pain ensues so the child will withhold it more. It can be a vicious cycle for which it can take months to overcome. My daughter had to see a Pediatric Gastroenterologist when she was potty training and had constipation problems. HE said this is common in potty training Toddlers. He said, you have to let the child go at their own pace. Let them poop in a diaper... since they are not yet wanting or able to go in the toilet. No rewards/punishments will "make" them go. And you do not want the child to get complications because of pooping. HE said pooping in a toilet then becomes an "emotion" based and biological based problem... if it becomes a battle. For my girl, we did NOT force her to poop in a toilet... but as she was progressing in toilet training... she just got anxiety about pooping in a toilet.... so we let her go at her own pace. But she got constipated... and we then had to treat her with things per the Doctor's prescriptions. According to the Doctor... pooping attainment, in a toilet, can take MONTHS. The child is simply not ready. The Doctor also strongly advises against using "enemas" or suppositories in a child... although some do. It can be habit forming.
Are your twins taking Miralax everyday because they are constipated? If they are not constipated... they do not have to use that and certainly not everyday. It will not make them poop in a toilet.
Here are some links:
http://en.allexperts.com/q/Pediatrics-1429/2-year-old-hol...
All the best,
Susan