Have them make a train using 10 unifix cubes the same color. Then have them break it into 2 parts and tell you the parts. They can even play a game with a partner where one of them breaks off a piece and the other one has to guess how many they are hiding. It really reinforcing the whole and the parts concept.

Another way I like is to make a bead bracelet with a pipe cleaner and 10 beads (we actually begin with whatever number they already know the components of, and they practice the next number.) Using the same concept as the train, move the beads so that they are in 2 groups. Once they know the parts, let them keep the bracelet.

Last one- I use a ten-frame. It's a 2 column table with 10 boxes. Put objects in part of it- how many more do you need to make 10?

I know there are lots of ways, but those are my favorites.