M.R.
He probably won't recognize the difference. Here's a funny story I recall from my childhood:
In my neighborhood growing up, we always had one of the dads dress up as Santa and visit all the houses. On a Saturday afternoon, Santa visited our house right before we had to go to a family Christmas party given by my dad's work, which was about 45 minutes away.
So after we visit with Santa (who we knew had to visit the other houses), we load up in the car and go to the work party and guess who is there? Santa, but obviously not the same one from the neighborhood. I remember thinking to myself in my 4 year old way of thinking "Wow! Santa's sleigh and reindeer must be fast for him to visit all those kids and make it to the party on time!" I NEVER thought they were two different people.
The truth came out in my 20s when my mom and dad were joyfully recalling that story over a Christmas dinner. I had to laugh at myself for being so 'gullible'. I also found out that the Santa was actually the father of one of the neighborhood children with whom I was good friends in high school - I never even noticed!
The moral of the story is that you might not need to worry too much about it. Use the 'fast sleigh' excuse. If you're not comfortable with that, if there is a noticeable difference older then say "wow, Santa must be worn out from working so hard" or if the difference is younger then say "Looks like Santa took a nap and looks much more rested."
And, if I'm a bad person because I'm encouraging you to tell white lies then so be it :)