My child is 11 months 1 week and has blisters on hands, feet and thighs , she recently had fever, what would be the cause?

Hard to be specific: Hand foot mouth syndrome is caused by several strains of virus & can be quite diverse.Variation can range from no outbreak or fever at all to significant blistering in h/f/m/anal &up the legs &arms.Isolated lesions on the legs & arms without the typical grayish oval lesions on the back of the hands or feet likely represent something else.