Seeking advice.. ugrent

My nephew is 4 year old and 2 weeks ago we notice bruises on his legs, the doctor suggested blood test which showed platelets count at 7000.. his doctor gave him Corticosteroids for 3 days and the count went up to 67000 then he advised to stop taking it and test again within 3 days and his count went down to 42000. then doctor suggested another test within a week and in the 6th day he got 2 new bruises, next day he did the test and it's 7000 again, he was hospitalized yesterday and was given Intravenous Immunoglobulin, half way through he vomited twice, started shivering and got fever and loss of appetite, they stopped the treatment and did some blood tests, scanner.. his fever wasn't going down so they gave him an injection.. Now I was just off the phone with my sister, his fever in on and off and they stop the immunoglobulin treating whenever it's high.
what I want to know is, can he fully recover?
How long does it take?
if this doesn't work what is the next step?
what is the worst case scenario?
I am sorry for my English, I am seeking advise because I am worried sick about him.. Please anyone who has a toddler his age, share your experience with me

The good news is kids of his age have a well over 80% chance of having an acute ITP. That means ITP is just one-off thing and he will be in remission within 6 months to a year (Most kids recovered within 8 weeks according to our hematologist). Even though your kid fell into that 20% and become chronic, there are still many treatments you could try, such as Promacta, NPlate, etc. In general, kids are very resilient with low platelet. However, when he is under 10K, you need to watch for signs of internal bleeding, such as blood in urine or stool, severe headache, etc. We also devastated for the first few months when our 12 years old son got ITP. But just be calm and ask a lot of questions, life will be back into normal. You could also join a Facebook group, which is a bit more active. Good luck.

Nizar, my son was 3 when he got ITP, you can click on my profile and look at the early threads i posted to read our story (it has a happy ending). So, first, don't despair, although I know this is tough. His young age, male gender, and low count at presentation are all associated with higher likelihood of full resolution of ITP if i recall correctly.
Now as for the IVIg reaction, he may need a different batch or different brand. It is a biological product so it can cause reactions, including allergic. My son was pre-treated with Benadryl before each dose, which was handy because it also helped make him drowsy so he slept through most of his treatments (we also tried to time it during naptime or nighttime if we were staying in the hospital). If your nephew was not pre-treated with an antihistamine, you may want to ask about that. I believe some kids also get an anti-nausea med before treatment. Good luck to you and your son!