If it makes you feel better, Miralax is pretty much just concentrated pear juice. They take the part out of the pear that works as a laxative, and they concentrate it. It's pretty benign as rx meds go.
That being said, there are some other alternatives:
-- magnesium. My friend gets some natural mag from her chiro that she mixes with water and gives to her preschooler. If she doesn't give it, the girl won't poop. Milk of Magnesia also works very well and it's safe to use long-term.
--pears of any form. Juice, purees, canned, fresh.
-- prune juice hides very well in fruit punch
My first dd got this as a toddler and called the juice "tastes like raisins" juice.
-- Metamucil "cookies". My dd liked the apple flavored ones. Give with lots of water. One cookie usually did the trick for her.
-- Benefiber is also effective although it's not as effective as magnesia and the other things at the top of the list.
Good luck mama!