Should I bring in a sapling crepe mettle plant for the winter?

Depends on where you live, here on the Gulf Coast they are just fine outside all year long, as long as it get water each week. I would keep it out of direct north wind though and if you have hard freezes where you live, maybe sink pot and all in the ground and let it winter over that way.

Crepe myrtles can and do tolerate pretty cold weather. Since yours is very small and in a pot, you'll need to decide. If the temps in your area stay below freezing for more than 5 days in a row - you should probably bring it in if you can. Crepe Myrtle varieties are many, but they will drop their leaves and go dormant in the fall. Bringing it in a garage or protected area will also work - depending on how low your temps get. And, as MJB said, don't forget to give it some moisture every week or so during its dormancy.

I live in Region 6 and my new crepe turtles made it through the first winter. Mulch heavily to protect the roots and try to protect from fierce winds and you should be ok

First of all the name is Crept Myrtle. Crepe myrtles range in size from dwarf selections that grow less than 3 feet tall to several that reach upwards of 30 feet. Knowing the mature height of a plant before you buy it and planting the proper size for the site will save you much heartache and backache in the future. If you're in the Midwest, you should also look for selections that are extra cold-hardy. I live in zone 6a-6b. I have had three sizes of Crept Myrtles for 28 years.

I am not sure what zone you live in, but if there is any fear of frost or freeze I would say yes. Full grown in ground crepe myrtles are known to survive, but in a pot is much less likely. This is especially true since yours is so young. I hope you have a nice sunny spot for it this winter indoors. When we started our cherry tree in a pot, we brought it in 2 winters, now it is doing great in the ground. We put it out a few hours a day to toughen it up before planting it in the ground one spring.