Hi,
Thanks for writing to us.
I have gone through the image attached. It could either be blister beetle dermatitis( caused by an insect blister beetle) or contact irritant dermatitis( caused by irritant like detergent soap, medicine, dettol, savlon etc).

The treatment in both the cases remain the same. Clean the area with warm water and apply a steroid antibiotic cream. in couple of days, the lesion will dry and resolve. If itchy take an oral antihistamine like cetirizine. You may also fet the fluid drained from big blisters by using a sterile needle or syringe.
Hope that answered your query.
take care

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Hi,
Thanks for writing back and accept my apologies for delayed response.
Brown recluse bite or spider bite is just the same as brown recluse is a type of spider. It could be a possibility too. In mild cases it is characterised by pain swelling, blister formation and ulceration of the affected area. In severe cases can lead to fever, chills, vomiting, joint pains etc.
Let me tell you, developing a blister at a site of insect bite is due to toxin produced by an insect and it can happen with bites of multiple types of insects. So we can keep it simple as insect bite induced blisters.
The management would remain the same in blister beetle dermatitis or recluse spider bite ie
clean the area with warm water
apply topical steroid antibiotic cream
if itchy child may take cetirizine. If painful, he may take syrup ibuprofen.
if blisters are too big, drain the fluid using sterile needle.

if there are any systemic symptoms like fever, joint pain etc make it a point to contact health care provider. usually brown recluse bite ulcerates, if there is no ulceration; it could be simple blister beetle bite.

hope that answered your query.
Take care

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