Hi there. At the outset, this child needs be evaluated by a dermatogist if not done so hitherto. The blisters could be one of many things but if one were to put the calf pain & blistering together, one wud have to ask if there is a stomach pain of sorts or cramping. Porphyrias cannot be ruled out & blood & urine & feces investigations need be carried out. It does not look like a mosquito bite reaction from your description but yes, allergic contact dermatitis
after exposure to garden products or/& aggravated by photoexposure need be borne in mind & due precautons taken with sunscreens et al recommended by your dermatologist
on the ground. There are some other childhood bullous dermatoses
that come to mind & an ideal test would have to be a skin biopsy
of an intact blister followed by histopathology & immunofluorescent studies that should be available in a major hospital near you. Cheers & Good luck!