RE: What's the earliest age you can start using a cart cover?
Nope - he's way too young for a cart cover. He will just slide down and slump (even if you prop him up with pillows). IMO, the cart covers don't help the babies sit upright at all, they just give them a cleaner, more comfy place to sit. Colin could sit up at 7-8 months but still slumped and slid in his cart cover.
If you think about it, the strap on a cart cover is the same as the strap that is in most carts already (a waist strap). Have you tried the infant seat attachments that are on some carts? Throw a blanket over it to give him a clean surface to sit on, and at least he's comfy and safe.
Single mom to
DS ("twice exceptional") - September 2002
DS - February 2006
DD - July 2009
DD - July 2009