A 5-year-old boy comes with overnight petechial spots 2 weeks back he had a history of abdominal pain and no hepatosplenomegaly. Diagnosis is –
Petechial spots without hepatosplenomegaly in a 5-year-old boy suggest the diagnosis of ITP.
About other options
Acute leukaemia

Acute leukaemia will give features of involvement of all the three lineages i.e.
anaemia (erythrocyte involvement)
fever (due to neutrophil involvement)
bleeding (due to platelet involvement)
Moreover, splenomegaly and lymphadenopathy are usually present in Acute leukaemias.

Aplastic anaemia

Aplastic anaemia too will present with features, characteristic of involvement of all the three lineages i.e. severe anaemia, fever bleeding.
Aute lymphatic leukemia
Aplastic anemia
Idiopathic thrombocytopenis purpura
Acute viral infection