I've moved abroad a few times so I'm not the type to discourage people from trying something new and I understand the appeal of wanting to be elsewhere.
Yes, salaries are much higher in the US. They need to be -- Americans on average produce three to five times the carbon emissions of the average Brit. You'll spend a lot on food, a lot on petrol (it's cheaper but you'll suddenly find yourself spending hours a day in your car just to get the kids to school, go shopping, get across town, etc.) and a good 10-20% of your wage will go on health insurance. That's just to have the insurance, you'll also have co-pays and deductibles, where you have to pay the first, say, $10,000 of healthcare costs per person per year before your health insurance will start paying out. Your house will be much, much bigger than your house here, but if you're in Seattle, for instance, it will also cost more (assuming you don't have a big house in a leafy area of London at the moment). That's not true for all areas of the US, the west coast is the most expensive, no idea what Maine prices are like, or why you would move there.
If your kids are school aged, you'll have to learn to live with The Fear. You only hear about the bad school shootings, but they happen all the time. And even when they're not happening, there are lockdowns at the average school a couple times a year because someone threatened to bring in a gun or a bomb, so you'll be in a complete panic every once in a while because there's a "situation" even though in the end it was okay. If being panicked about your kid maybe being in danger is ever okay. All the moms I know these days shrug their shoulders throughout the school year and say you can't live in fear, but then admit they're so relieved when summer vacation starts because they can finally not worry about it for three months.
Speaking of, summer vacation is three months long. You will spend another 10% of your income on endless summer camps and activities for your wee ones because you'll probably need to actually go to work. Americans work, a lot. Holidays are short, paid time off is minimal, and if you have another baby you'll be lucky to get six weeks off. Work life balance is not part of our ethos.
I love America, I really do. 😅 I love the varied, beautiful landscapes and how kind everyone is (for the most part). I hate the culture of consumption, of violence, of entitlement. I really hate how every town looks the damn same because of the same chain restaurants, the same grocery stores, the same Targets.
The PNW is really beautiful, it's where I would move back to if I was forced to go back. But it rains, a lot. I always joke when people here ask me if I was shocked at the weather, because it rained a lot more back home than it does here. Still gorgeous, though! And you can go hiking and skiing in the mountains even in the rain/snow.
Still... I miss my family so much, but I will never go back.