Regrouping is a difficult concept for some children to understand. Using manipulatives helps, but I find that using money makes it easier for the children to visualize the exchange of ones, tens and hundreds.
It also connects them with real examples of Math in their world.
When referring to trading ones for tens and tens for hundreds, I tell the students that they need to go to the bank. They need to deposit their pennies and get a dime or deposit their dimes and get a dollar.
When referring to changing a ten into ones, I use the analogy of going to the bank and trading a dime for 10 pennies.