Preheat oven to 400. Cut acorn squash in half with a large knife and scoop out seeds. Put in a 9x13 pan with some water in the bottom to keep the squash from burning. Place skin side down in the pan. Poke holes in the sweet potato with a fork and place on the oven rack next to the squash pan. Cook 1 hour give or take. You should be able to easily pierce each item with a fork to know it's done. Take out from oven and let cool about 15 min.
Using a blender, food processor or your fav similar gadget, scoop the fleshy part of the squash out and pulse, adding breast milk or formula to thin it out and make it creamy, to a puréed texture. Put in to small containers* and refrigerate or freeze. Clean out the machine and repeat process with the sweet potato, removing the flesh from the skins and pulsing with breast milk or formula to desired consistency. In freezer these will be good up to 3 months. I put two in my fridge and six in my freezer. I spent $2 total on the squash and potato which comes out to $0.25 per serving compared to $1 per jar of baby food at the store!
*use an old ice cube tray if you don't have access to enough small plastic containers and freeze the food in cubes, then plastic storage bags