My baby is 9months have had a fever since last thursday and have red patches all over hus body any idea of what thus could be?

Infection,see md: Please see pediatrician to determine if this is bacterial or viral infection which is accompanied by a rash. The combination of fever and a rash is highly suggestive of an infection amd should not be ignored.

Roseola?: If the fever lasted 2-3 days, then went away and the rash appeared, then it is from roseola (a viral infection). If fever and rash are present together, then a doctor needs to see your child as the possibilities are too many to answer here.