My six year old son has one descended and the other retractile testicle,it moves back n forth and is a little smaller then the other descended testicle.is this normal?

Hard to guess: His pediatrician can take a look to decide what to do. Testes don't have to be matching in size exactly, but if one is a lot bigger than the other, then something may be wrong with either one (the one that is too huge, or the one that is too tiny). If a testis is retractile and tends to stay up high in the scrotum, the doctor may ask a pediatric urologist if anything needs to be done at age 6y.