Can this wagon hold a child (or children)?
Sure you can pull a child in the wagon and have let children lay in the cart to sleep and then pulled them to the car after a long night of softball. Use common sense. Don't park it next to a cliff with your child inside or on an incline without holding the thing. :) Use it properly and it will be one of the best investments a "ball" family can make.

Are the wheels rubber? How would this handle a gravel path?
Wheels are rubber. They would have no trouble on a gravel path. you can taken it to the beach and on picnics in the park and have never been disappointed in it's performance.

What are the dimesions of the carrying space--not the cart overall, but the carrying space itself (L x W x H)?
2140W-----------L =30.3, W = 17.3, H = 10.6
2140RRB-------L =30.3, W = 17.3, H = 10.6
2140RSB-------L =30.3, W = 17.3, H = 10.6
2133RL---------L =40.1, W = 17.3, H = 10.6
2133M-----------L =20.2, W = 14.9, H = 10.6
2133L------------L =32.7, W = 14.9, H = 10.6
Sides can expand slightly, front and back is fixed. you can use this for everything, carrying in groceries, luggage on vacation, very handy.

Useful for beach use?
It would be very useful for the beach. The wheels are sturdy and move easily. You could fit a cooler and beach chairs. It will hold 220 pounds.

Does this require assembly?
No assembly required and I wish you would have known about this wagon along time ago, it is awesome.

Where is this wagon made?
The Cart is produced in china.