I've noticed there are a few other threads on this topic but they haven't been posted on for a while. I'm wondering if there are any other parents out there who are dealing with this and have been for a long time. We've been dealing with this for 3 years now and my son is now 5.5. We started off on lactulose and until recently he was on movicol. With the help of a Dr in the US our son is now taking ex lax chocolate squares and for the first time in 3 years is self initiating to go to the toilet. Reading other threads I understand people have had success with Movicol however it caused my son to have daily (small) soiling accidents as he tried desperately to withhold but couldn't completely do it. We found that for Movicol to work there was a fine balance. Too much and we got soiling and too little and he wouldn't go at all, so great was his ability to withhold!
I think there is not enough awareness of this problem that in actual fact so many children and families deal with. I know first hand how soul destroying it can feel if you're dealing with a particularly difficult case.
We read the book 'Constipation, Withholding and Your Child' way back, and in fact our consultant is the Dr who wrote the book!
Anyhow, I'd be interested to hear in other people's experiences where you've found it difficult to get on top of this problem and it's been ongoing.