Oh Nic, I am so sorry that you are going through such a very tough time! Just a little longer and things WILL start to improve! Just keeping reminding yourself that Matt and Ella are on the road to treatment and recovery.
As everyone has said, you can't blame yourself. My son was diagnosed this spring and I am sure that his trigger was all the ibuprofens (on doctor's advise) he took over the winter to relieve back pain from hockey. I think back and wonder why didn't I ever think that it was too many ibuprofens, why didn't I send him for more back massages, why didn't I just keep him from a few games or hockey altogether??? But, his GI has said that if it wasn't the ibuprofen, eventually, it would have been something else...
I just want to share something that may help the parents of young children here... when I was between 5 and 7 years old, I was diagnosed with juvenile osteoporosis. Its very rare (at the time, the children's hospital in Toronto had only had 9 cases in its history) and it took a long time before the diagnosis was made. During those years, I was in the hospital for weeks, if not months and, at that time, parents were only allowed to 'visit', no 24/7 attendance. Often on my own, I was poked and prodded by countless doctors from countless departments and some of the pokes and prods were painful. Prior to the accurate diagnosis, errors were made in treatment - 'it's all in her head, she wants attention' was one diagnosis - off to the psychiatrist I went (no help), another treatment worsened the condition (or allowed the condition to worsen) to the point that I could no longer walk at all, one nurse decided to take matters into her own hands and, after an excursion with some patients to the hospital's yard, declared that I could 'walk on my own if I really wanted' and left me outside alone. I suppose she forgot about me and it wasn't until my mom arrived hours later that I was found, terribly thirsty and sunburnt. I was eventually diagnosed and treated, altho it did take a few years for my body to completely rebuild the bone density and muscle lost over the years. BUT, with all that, my memories of my childhood are only HAPPY ones!!! I've never remembered the the painful pokes and prods as being any more 'traumatic' than when I fell and required stitches as a teen. I may not have the same memories of being 5-7 years as the typical person, however, I remember attending shows and events at the hospital that my friends at home couldn't attend, my memories include hospital playrooms filled with every toy imaginable and doctor's visits being no more than 'interruptions' to my time in the playroom. I remember feeling special because so many people always came to visit (and brought gifts! LOL). I remember numerous follow-up visits to the hospital as an outpatient but I remember that each time we went into the city for an apptmt, my parents would take me for an ice cream or just a walk downtown (exciting for a 7 year old!). Even after spending two years seeing doctors, not being able to walk, not being able to attend school very regularly, taking medications or treatments I didn't like, these memories did not replace HAPPY memories, they are just part of my childhood just like losing a childhood pet (certainly an unhappy memory but not overshadowing all the happy ones).
I hope this alleviates a little of your concern that your child will not have a 'good' childhood. I was fortunate that my condition eventually led to a full recovery, however, my childhood was filled with hospitals, doctors, needles and, as far as I'm concerned, it was still all good!