Today was my last straw though. The girls and I went to Target to get my prescriptions and due to my above stated hatred of their two seaters I opted to put them in a cart. Kendall sat belted in the basket seat and Seren in the cart. Seren loves to stand up and I repeatedly placed her on her bum and told her to sit. And she would almost immediately stand up again and grin at me. She knew I didn't want her to stand but she didn't understand why. Not until it was too late. We were at the prescription pick up counter and Seren was standing in the cart that wasn't moving, the pharmacy tech asked me a question and I moved the cart to hear her and out toppled Seren. Flat on her back on the hard tile of the store. I dropped everything in my hands and picked her up in an instant. I couldn't have felt more guilty. I was beyond grateful and a little embarrassed when she clutched me and started wailing. I looked her over for injuries and apologized to her over and over for being a moron of a mother. Things happen. I am so grateful she wasn't seriously hurt. And now, researching an idea to make a seatbelt for the cart, and reading about the number of children who end up in emergency rooms from similar falls (from the cart or basket seat) I am even more grateful she is okay and also embarrassed that I let it happen.
Yes I'm the moron who let it happen. But I'm still pissed off at stores for having very little or poor solutions to the problem (especially when twins are so much more prevalent these days).
Don't let kids stand up in carts...ever (moving or not). Find a better way. When I find or invent my better way I will let you know. Until then I will be shopping with our stroller or in the hours that hubby can keep one or both girls at home.

