Is it normal for 3 years to have arm pit odor?

Yes, it's normal for children around the age of 3 to start developing body odor, including armpit odor, especially if they are active or if it's hot outside. However, significant changes in body odor can also indicate other factors, such as diet or hygiene. If there are concerns about excessive odor or if it is accompanied by other symptoms, it may be a good idea to consult a pediatrician.