I read somewhere that the die off isn't as intense with children because their guts aren't usually as damaged as adults guts are.....
In any case, we didn't notice anything crazy when we did a gut healing with ds when he was about 7. Like JaneS mentioned, we eliminated a new food allergen (which prompted the reason for healing) and then also reduced a lot of, but not all, grains, yeasts, & added sugars/fruit for a good 3 months. We made sure that we were doing good probiotics and digestive enzymes. We were already doing Vit. C, magnesium, fish oil, and a good multi-vit, but also added in zinc at this time. Those supps are still in our repertoire.
I don't think gut healing is fast, so I'm not sure how quick you think it could go. Within a month, I could tell a big difference in ds' facial color, but that could just be due to the fact that we took an allergen out of his diet. His gastro-intestinal issues were under control in 3 months, but I guess the long term thing is that he has only been sick with a stomach bug once in the last 1 1/2 years. A lot of the dietary changes that we initially made have stuck, so what was going to be a 6 month deal, has now become a way of life. We aren't as diligent about it as we were during the initial months -- so if we splurge here and there, it's ok. DS also self-regulates well; he avoids processed sugar on his own and doesn't go crazy on grains/breads.
I read an article once about someone who did a modified GAPS diet with her family. It took about a year, but she had very good results with that.