Your laptop chargers should work just fine over there with a simple plug converter: those are nearly always rated 100-240V. You can also buy American cords for the laptop chargers which should just plug straight into the adapter. Phone chargers, you can buy a new American plug from the Apple store or a Walmart / Target for the USB cable, and until then, whack a plug converter on the UK plug or charge through usb only.
American computer keyboards are aligned slightly differently: e.g. the " and the @ symbols are swapped around, and there's not usually a £ or € symbol on the keys. If you have any Bluetooth keyboards in your house, bring those with you. You can re-learn typing, but it's annoying and slows you down if you need to start work straight away.
Bring your favorite tea. I've heard Yorkshire Gold mentioned in an early episode of Homeland, but I don't know how available it is. If you're stuck, you can find Twinings English breakfast in the bigger supermarkets; that's what my husband has for his morning tea when he visits my family with me. Lipton is dire, and in the South, is really meant for brewing iced tea, not hot. You can find an electric kettle though; my parents have one. There are lots of herbal teas available in the stores.
Bring your favorite biscuits and chocolate: little comfort foods for when you feel homesick. Americans don't really do digestives unless they're in the import section of a store, and British chocolate is still a lot nicer than American (thinking Cadbury's and Galaxy, as opposed to Kit Kat's). Bring your favorite cereal for the first week. You can find porridge oats and shredded wheat easily enough, but I can't remember ever seeing Weetabix when I've visited back home.
My parents have moved around the USA a few times in their 50s. Clothes got pared down with each move. Furniture is easily replaced secondhand. They've gotten some really nice pieces through Goodwill and other thrift stores. There will be an online secondhand market too. Yard sales also used to be popular where I lived (Massachusetts); they're a bit like car boot sales, but done on someone's lawn.
American bed sizes are definitely different. A queen measures closet to a UK king, a King size is more like a UK superking, and then there's a "California king" I think. A "full" US bed is closest to a UK double (I think!). The advice about bringing duvets is good though: my family's and friends' bedding is more about layering fitted and flat sheets with blankets and a patchwork quilt or thin comforter. I like the duvet+fitted sheet version of bedding so much better!
Get your toddler fitted for a new pair of shoes just before going. The approach to children's feet isn't the same in the States. I can't remember ever seeing an equivalent of start rite or Clark's with specialist shoe fitting when I've been in America with my kids: just high street selection.