One of the chains here in Tucson has them. I don’t know if they charge, but they do have a play area the kids can stay in while the parents shop.
But you’d probably need to take about 57 of those little wipes they have for cleaning your cart handles and wipe that sucker down first. Ew- imagine the germs that must linger in those places.
They are attended. Probably the attendants take care of keeping things wiped down.
EDIT* This is from the store’s FAQ’s:
Q. What are the cleaning procedures for the Cub House?
A. The Cub House is cleaned and sanitized continually throughout the day, as well as every evening when the Cub House is closed.
I have a strict rule in this household: I will take one (1) child with me to the grocery store at a time. ONE. And that child will not be between the ages of 2 and 4. If there is some kind of grocery-related emergency that forces me to violate this rule, we do a tactical strike; in and out, moving at top speed, spending no more than a total of 15 minutes inside the grocery store.
Oh, and in this family nobody sits in the cart unless they are buckled in. I am generally pretty touchy-feely with my parenting, but in the grocery store I morph into some kind of cross between Genghis Khan and General Patton. Show no remorse, take no prisoners, and brook no resistance! It is the only way to survive.
My almost five-year-old has always been really small for his age. Until very recently, he’s liked sitting in the seat part of the grocery cart, and when he did, he thought it was cool that he knew how to buckle the strap, so he did.
Once in a while, he’d ask to sit in the cart part. If I let him (which was pretty seldom), the rule was he had to sit on his butt at all times. If I caught him even sitting on his knees, he had to get out and either walk with me or sit in the seat part. He caught on to that pretty quickly, and I only had to pull him out of the cart once for trying to get up. Granted, he is a remarkable child so far, so loving and affectionate, rarely defiant and an absolute joy for us as parents. I’ve seen others struggle constantly with their children in social and public situations, and I wouldn’t want to presume that what works for me would work for anyone else.
One thing I’ve never let either of my boys do is ride the cart by laying down on that very bottom rack. I’ve always had visions of crushed hands/fingers, mangled arms or legs, hair getting caught in the wheels, etc.
It doesn’t matter anymore anyway. He seems to be losing interest in sitting anywhere in or on the cart. Lately, he’s taken to holding on to the cart and/or walking next to me.
They have that in the parking lot of Santa’s Villiage in Jefferson, NH, right down to the safety doors on each cubby. Oh sure, they painted pictures of dogs on the sides of the cages, but we all really knew they were to stash kids too young for the rides in.
The grocery store with the gigantic cars on carts also has a Kid Park – a mini-day care, as 'twere. Sign 'em in, and you have a supervised place for your kid to romp until the shopping is done. I loved it. My kid loved it!
Unfortunately, he “aged out” when he turned 10. And now that he’s a teenager, the dangers of taking him shopping are even more gruesome. What is this 2 lb. box of buffalo wings doing in my cart? “Mom, I just wanted an after-school snack!”
Bad description, sorry. She’s got her arms around my neck, I’ve got one arm around her.
Okey dokey. 
Mom would make me ride on the bottom part when I got a little sister that took my spot. The carts at the store we shopped at were shallow and there was enough space for me to sit like a sack of potatoes until I was 7 or 8 years old. I remember being really bummed when I tried to cram myself under there one day and I didn’t fit and I had to walk. 
I used to ride down there when I was little – the one grocery store we visited had the cart part high up enough that a kid could sit up under there. So my mom let me – as long as I kept relatively still and didn’t stick my fingers or feet into moving parts. I loved that.
HockeyMonkey, that’s where I sat too!
We used to have one in one of the stores until a remodel did away with it probably seven years ago. It was great since once the kid stopped fitting in the seat part, they were old enough for the “play area.”
To this day (my kids are nine and ten) I try and leave kids home when grocery shopping. Fortunately, between daycare, a husband and a very involved grandma, I could shop solo more often than not. The worst were the trips we’d make as a family when the kids were three and four or four and five. Two adults, two kids in a store. The store had “junior shopper” carts - so a three year old pushing the little grocery cart. Yeah, this was a good idea…
Don’t be silly. Of course you leave it cracked a milimeter. And you give double shots of NyQuil to the kids, so they can be relaxed and not panic just because it gets a tiny bit warm.
When I got too big for the seat my mom would put me under the cart. Do people not do that anymore? I never see it. (Is that bad? I guess it’s probably bad. Everything is bad these days.)
I used to yell at her to hurry up through the cold sections, because under the cart it’s really freaking cold in the meat department and the dairy aisle!
Really big shopping cart. Really big kids. http://www.youtube.com/watch?v=7jfg08IA1W0
That was my favorite riding place at the grocery store also. But these days I think that the basket part of the cart must be a lot bigger than the ones in my childhood, because I remember that even as a 6-year-old, I could sit fully upright underneath the cart, but my own 6-year-old would never fit under there unless he were lying down, and then his feet would be hanging off the back.