There won't be any questions entering Mexico - but there will be when you re-enter the U.S. Make your trip smoother by remembering to bring documents.
Here is what the U.S. says they want to see when you re-enter the U.S.
For U.S./Canadian citizens, there are two options: a one document or an alternative, two document requirement. (For participants who are citizens of other countries re-entering the U.S., see the second reprint below.)
U.S. entry documents required from citizens of Mexico or any other countries other than Canada and the U.S.