S.D.
This is very short lived common in 2 yr olds they are starting to learn more say more other than repeating the same thing over and over they can talk in conversations tell stories short to longer sentences it's just their brain isn't able to spit out everything at once so they stumble it's like learning how to walk it takes practice and soon it'll be a thing of the past.However just to throw this out there if he is reversing losing anything that he has mastered like talking walking sitting playing whatever it is then yes I would be concerned.Just tell him to think what he has to say slow down.