As adults, digit placement is second nature: ones, tens, hundreds, thousands, etc. It’s easy to forget that the way we now use numbers was an important cultural invention. And it’s easy to forget how hard it was to learn digits as a child. One of my biggest surprises as a homeschooling dad of a kindergarten-age child has been seeing what a conceptual leap it is to grasp digit placement. It helps enormously for kids to see visually what we’re talking about.
Of course it’s easy to make groupings of ten coins or whatever. I’ve used wooden cube blocks to illustrate two-digit numbers. But doing ten stacks of ten, and then ten stacks of a hundred, can be a challenge. That’s where Perler beads and pegboards (paid links) come in. You can get a large set for around thirty bucks and then iron together sets of ten and a hundred. (Or you can save some effort and spend over a hundred bucks on Montessori “golden beads” (paid link) if you prefer. There’s also a lower-cost foam option (paid link).) You can also do art projects with the Perler beads if you’re so inclined.
Update, June 28, 2021: Although I do like the Perler beads for visualizing big numbers, practically speaking, I turned to the foam blocks for routine instruction. To my mind these are a must-have item for beginning math students. The beads are a little too small for counting; the blocks are just right. It occurred to me that you could also just buy a jumbo pack of wood blocks and glue them together into rows of ten and squares of a hundred. But the foam blocks come cheap and ready-made.
You can also make some great counting and adding kits out of Perler beads.