28 months boy have 4-5 beats ankle clonus in both side since newborn,without other symptoms.he have a good milestone, he can walking-running normally.

The significance of: ankle clonus in infancy is not reliably known and relates to the number of beats (>10 seemingly important) and persistence at advancing age. The fact that your son has reached developmental milestones normally is very important. I would, however, have your son followed by a good neurologist as there are possible issues down the road. Good wishes:)