I don't know how to do links, so I've just copied and pasted what I wrote before. Hope it is helpful.
"I've posted this before, so you may have already seen this, but if not, this is I dealt with my DD (3 1/2) who would only poo in her pants.
I had tried rewards, reminding, books on the loo - nothing worked. I went to have a chat to the deputy head of my DD's nursery and we hatched a plan. It worked so well that that the problem resolved itself almost instantaneously.
OK, this is what we did. It might not work for you because your circumstances might be different. I admit I was sceptical of it working for us, but it really did. Incidentally, DD wasn't constipated at all and the issues hadn't started around a period of constipation. I think this would make a difference in how the issue should be approached.
- I stopped giving any reminders about going to the loo. Absolutely none - very difficult to do! I completely left it up to DD to make her own decision.
- I started saying, in a very casual and relaxed way, "Mummy and Daddy do poos in the loo, all the children at nursery do poos in the loo and you need to do poos in the loo to".
After a day of this, she did her first poo in the loo for four months. I fell over backwards. There were one or two accidents over the next few days.
- If she pooed in her pants, I waited for her to come and tell me. (Previously I had pointed it out to her.) I then said "Let me know when you want to come and get changed" and walked away. This was to get rid of the usual game where DD ran away while I try to get her changed.
- She had to help to clean herself up i.e. she helped to pull pooey pants and trousers off, and cleaned herself with wipes. I ignored her as much as possible and got on with cleaning yucky pants. I didn't comment at all, although did help a bit to get her clean at the end. I didn't give her any praise for wiping herself but was not nasty at all. It was all just very matter of fact.
- I gave her new pants and trousers and let her get dressed by herself. Again no praise but no nastiness.
Throughout I tried to maintain a zen like calm!
It was only while dealing with pooey pants in the method I descibed above, that I realised how much attention she had been getting from me previously when she pooed in her pants. Previously I really thought I was giving her lots of praise for doing the right thing and ignoring when things were going wrong, but I just wasn't. I was cleaning her up through gritted teeth and making lots of cross, annoyed comments. Also, reminding her lots and lots, which of course meant she know exactly which buttons to press when she wanted my attention.
Really hope this helps."