The cause of the blister-like red bumps on your baby’s arms may be chickenpox, hand, foot and mouth disease, and so on. 1. Chickenpox: mainly due to infection with varicella-zoster virus. It leads to the appearance of maculopapular rash, herpes and clear blisters on the skin of the baby’s trunk and face and other parts of the body. At the same time, it can also be accompanied by itching, fever and other symptoms. 2. Hand, foot and mouth disease: When hand, foot and mouth disease occurs, it can cause similar red bumps and blisters to appear in the oral mucosa. At the same time, the buttocks, knees, and palms and feet area, there will also be similar blisters appear. When blister-like bumps appear on the baby’s body, it is recommended that parents must be vigilant and take the baby to the hospital as soon as possible in order to clarify the cause of the disease and give appropriate treatment under the guidance of the doctor.