For case 3,I will think of nasopharyngeal carcinoma with differential of rabdomyosarcoma, because of location, size of the mass and age of the the patient.
My treatment modality will include laboratory examination like complete blood count, then biopsy and histology and may be CT/MRI if there are other features suggestive of metastasis.
My mainstay of treatment will be radiotherapy.
For case one i think i will need further history and examination, like the exact location, character of the abd mass, and abd scan.
I would rather seek the input of Dr @endopediatria in this particular case management , with her experience in the field of pediatrics and also an erudite lecture in the field i believe she had a first hand experience with the patient.
@omaqiin im curious to know why you are sticking with nasopharyngeal carcinoma?
Can you give reasons ..
@omaqiin in healthy children the first probable diagnosis is ectopic thyroid as explain @elvigia. In this case was confirmed with thyroid gammagram. Her thyroid tests were normal. Of course carcinoma is a diffetential.