Making a large-bead abacus is simple, but can be a little tricky.
First, find a wire hanger (this part is not always easy, as there are so many plastic hangers now). We did have quite a few wire hangers, so finding one was easy. Also, you'll need some large wooden beads-- the kind that are used as lacing toys. They need to have a fairly wide hole.
Then, untwist the wire at the top, so both ends are open. Straighten out the end without the hook, so you can put the beads on.
Slip beads onto the wire, and past the curve so the rest on the bottom of the hanger. If you make 5 beads of one color and 5 of another color, this makes it easier to recognize larger numbers shown on the abacus.
Then retwist the wire at the top (the trickiest part; once taken apart sometimes it doesn't go back together exactly like it was before-- but if you work with it a little, jiggling and bending as needed, the two wires will twist together).
One more thing-- the hook needs to be bent inwards, so it won't be poking out, as a safety precaution.
Voila! Now that the abacus is finished, you can try it out; your young preschooler will enjoy moving the beads one at a time, to count from one to ten. You can also work simple addition and subtraction problems by sliding the beads.
If you'd like some easy, extra-large-print math problems that are all ready to print out and use, take a look at Preschool Math: Number Tiles. In this one e-book, there are 4 sets of 20 pages each-- half the pages are for adding, and half for subtracting. Once printed out each set can be reused as needed, so this is a resource that just keeps going!