Need help with pediatric care plan!!

How was his diet?

If he was not eating due to feeling ill you could use imbalanced nutrition.

I think your anxiety is really good. You would need to change the way you explain things because he is so young. Also having the mother not be around when he is having an IV so that the nurse is the "bad guy" and when mom comes back she is the "good guy" and his source of comfort. It is important to not have this child feel like they are being punished for being sick. So I think you should use anxiety.

I do not know about the hyperthermia diagnosis. It depends on how high the fever was. But since he was afebrile you may not want to use it.

If he doesn't have hyperthermia, well, you can't very well diagnose hyperthermia, can you? Nope.

Note, you are not doing a nursing plan of care for Group A Streptococcus infection. No, you are not. Really. Nursing diagnosis is independent of medical diagnosis. You are searching for nursing diagnoses that apply to this child who is in the hospital. What did you assess with him besides his rash? Behavior? Fluid and food intake? Separation from his mom? Clearly not fever. Remember that the family is part of your care, so you can look at the mother's understanding, behavior, and so forth too.

Did you possibly look through your NANDA-I 2012-2014 to see the myriad other choices that could apply to a two-year-old admitted to a hospital, and his mother?

On just a cursory review I'm seeing a lot of possibilities, depending what your assessments told you. Don't try to pull diagnoses out of the air based on what you think might be there. Get the book, or you're cheating yourself out of the best resource there is for this sort of thing. $29 with free two-day delivery for students from Amazon, or $24 to download to a Kindle or such.