Don't get nervous because as you have mentioned it doesn't seems that he has any weakness in the leg.
There are some physiological variations in children from adult. Like bowing of lower limb( tibia
) is common during 1st year of life, bowlegs ( increased gap between the knees of two legs) are common during second year and knock knees ( decreased gap between two knees) between 3 to 4 years.
I would suggest you to consult an orthopedic doctor to rule out any significant abnormality if there is any and also get an investigation done to rule out calcium or vitamin D deficiency as this is very common now a days and can cause weakness or leg deformity