I could write a book on all of the issues we had with our daughter and these exact same problems. I'd like to say it's an easy issue, but it's not. It took us years to get our daughter over her problem. But it can be done! In fact, our daughter is now 12 years old and goes BM almost every day.
We didn't get there overnight, though. We went through all the medicines that help with these issues until she was 5 or 6. When she was 7, our family switched over to eating organic (everything, to include the fruits and veges we eat to the grass-fed meat we bought) and drinking reverse-osmosis water (to remove any and all impurities). We also discovered we all harbored various food allergies or intolerances (saw a naturopath and were tested) and took all of those food sources out of our diet. What a difference that made!
Once we did that, her system cleaned itself out, and now she never goes longer than two, maybe three days between BMs. She also takes a very good multivitamin (because the R/O water also takes out minerals, which need to be replaced), Calcium/Magnesium/Potassium/Phosphorus, Vit C, Vit D, a B-Vitamin Complex, 10-mushrooms (for her immune system), Florajen3 (a probiotic), Digestive Enzymes; in short, I've rebuilt her system so that it is healthy, not depleted in any vitamins, minerals, enzymes, or amino acids. We're working on "liking" our vegetables, which is a really big one for being regular, as well as making sure she gets enough fiber in her diet. In short, making sure she eats enough of all the different food groups, and not just the ones she likes (which used to be just grains/starches and milk).
A gentle laxative that's easier on the stomach than pharma drugs/laxatives is CALM, which is a magnesium-flavored drink. It will gently stimulate the colon and therefore, effect release. CALM can be found at natural food stores, your local co-op, Trader Joe's, Whole Foods, HyVee (and if their supplements section doesn't carry it, they can probably order it for you). My daughter still drinks some of this if she hasn't had a BM in two days.
You want to stay on top of elimination, so that it doesn't back up and completely fill up the colon track (been there; daughter did the same thing when she was 2). In fact, my daughter backed herself up again when she was 10; that time, I took her to a colon therapist, who gently washed her colon out. It worked and got her cleaned out. However, my daughter's decided she'd rather do what she needs to do to keep herself regular rather than having another one of those. ;)