Some carts work better than others, but you're right to be careful setting the car seat on top of that front part. If both of you are going into the store, I'd recommend just taking a stroller in unless you just need to pick up a few things. Do you have one of those car seat / stroller combo's? I used mine hard for the first few months... actually used it *as* a shopping cart a few times (putting a few groceries in a basket that I hung from the handles or shoved into the bottom of the stroller LOL)
