You’ve seen them in various projects that roll, toddle, and race. For anything ambulant, we highly recommend these fantastic plastic wheels, sold by Kelvin Educational. This post also includes instructions on how to make an official Pop Goes the Page wheel assembly for all your vehicular needs!
We discovered the 1-3/8″ diameter wheels while designing an event for Richard Scarry’s classic book, Cars and Trucks and Things That Go. The event was my son’s idea. He was 6 at the time, and told me the library needed to do “a program about crazy cars you can make.” Crazy cars we DID make, with some science thrown in to boot (details here).
To make a wheel assembly, tape two, 4″ plastic straws to the bottom of a box. Then thread two, 6″ wooden rod “axles” through the straws. We used BBQ skewers cut down to the proper size with pruning shears (and don’t forget to cut off the pointy end of the skewer!). Here’s what a finished wheel assembly looks like:
The wheels can be purchased from Kelvin Educational. Black wheels are product #990168 ($10 for 100); and color wheels are #990169 ($11 for 100). Warning! Sometimes, the wheels slide off the ends of the skewers. To remedy that, we hot glue foam beads to the outsides of the wheels. But Kelvin Education DOES sell the same wheels, same price, with “end caps.” So we recommend going with those (black #990170; color #990171).
In terms of sturdiness and versatility, these wheels are definitely worth the splurge! Here are some story time projects we’ve created with them…
Pig parade floats (marching band optional)
Hitting the streets with your pet skunk
A super sweet tissue box red wagon
An ice floe for a geographically challenged polar bear and penguin family
A bicycle for a well-meaning monster
A crêpe cart with all the trimmings, including a menu that allows you to order en français!
If these plastic wheels won’t work for you, alternatives include wooden wheels (a regularly stocked item at Michael’s Craft store), wooden spools, sized-down toilet paper or paper towel rolls attached to the bottom of the box, or poster board/card stock wheels glued to the sides of the box (like this awesome car, or this charming train).
We’ve made a lot of monster projects on the blog, but this is our first monster…on a bicycle! Where is he going? To find YOU, of course. And make a very special delivery.
The bike is a 4″ x 4″ x 4″ 
Use a small box or extra cardboard to create a small bike basket, then tape or hot glue to the back of the bike box. Not only does the basket keep the bike from tipping too far back when you’re pulling it, the basket holds something VERY special a little later. Finally, we have our monster…
Wrap a small oatmeal container with construction paper, then add arms, legs, eyes, ears, and horns. We added a little 
These were “kisses” the monster was carrying with him in his bike basket for you! Awww!
Color and cut the side doors and windshields from the template, then tape them to the box. I would, however, like to bring your attention to this very clever variation on the template. The kid bent the doors outwards, and drew a snowplow driver inside!
We provided 
The wheels and blade of the snowplow are black poster board. Add 2 yellow pom-pom “flasher lights,” a yarn pull string, and you’re done! We decided to add an extra challenge to our story time project in the form of these fabric snowballs. I scored a dozen packages of these on deep, deep discount this summer.
Kids were challenged to navigate our gallery, rolling the snowballs in front of the plow without losing them. Then they got to take some snowballs home!
Did you notice the little blue bow on the snowplow’s windshield? In the story, Gus ties his blue scarf on Walt to celebrate the little plow being “Number One!” We definitely wanted to capture that sweetness here as well.