My usual starting point for a young-ish family looking to FIRE is $1,000,000 in investments plus a paid-off house -- because $40,000 per year ($1m at the 4% rule) without having to pay rent is a secure, comfortable, non-extravagant lifestyle for a family. By that metric, you are perhaps 3/4 of the way there -- just need to build up a bit more home equity.
Day-care expenses will disappear quickly enough once the child is old enough for school (or once the parents are home enough of the time to watch the kid themselves), so I don't make too big an issue of those. But your special needs child requires a bit more planning. You haven't said much about the child's condition. It's not just the additional $12,000 per year in medical costs to consider, but the broader longer-term unknowns: Will the child need lifetime support and have trouble living independently? What are the long-term medical costs and medical insurance implications? You may want to carry more life insurance than most, and leaving behind a high-quality employer health plan might pose a lot more downside for you than for the average family.
If you were an average family I'd say that you were within spitting distance of FIRE -- 3-5 years, and most likely on the earlier side of that, with very little risk in taking a radical pay cut immediately if you really didn't want to keep doing what you're doing. But the better course of action now, until you provide more detail about the long term financial impact of having a special needs child, would be to plan on at both parents continuing work at current rates until you reach the basic threshold ($1m plus the paid-off house) and then have one parent continue work for several more years after that, at least.
Having a one-income transition period can also help with the positioning of your money, given how little you have in taxable accounts: The conversions to create a Roth IRA ladder, described by Laura33, are best done during years of no earned income, so you keep the taxes due on the conversion low or non-existent. But then you need a good sized taxable nest egg to tide you over until the 5 year waiting period is over. The next-best time to do conversions are when your income keeps you in a low tax bracket. Married filing jointly has some pretty large low-rate brackets these days, so there will be plenty of opportunity to get money into Roth accounts and favorable rates during the one-income phase. And it pays to continue to max-out your tax-deductible accounts while you are still a two income family, rather than stint on contributions to a 401k in favor of building up a taxable account, because even if you convert the year after contributing, when you step down to one income and pay taxes on the conversion, you will to a mathematical certainty have taken a deduction at a higher rate and then re-included the income at a lower tax rate, which puts you ahead.
To reduce this to steps:
1. Spend the next 3-5 years doing what you are doing: Earning a good six figure family income, maxing out all available tax advantaged savings, and pay off the mortgage aggressively beyond that.
If we assume this phase lasts 4 years, and assuming flat investment markets, you will have:
-Nearly $1.1m in retirement accounts.
-$81,000 in educational accounts.
-Around $165,000 in home equity.
-Around $68,000 in mandatory yearly cash-flows ($41,000 plus basic mortgage plus special needs child)
2. At this point, one parent retires and the other keeps working. This provides, I assume, a good health plan and at least $68,000 in after tax cash flow.
3. Even if nothing more is contributed to retirement accounts, you will still be improving net worth by probably $10,000+ per year given principal paydown on your mortgage (I'm assuming you'll still have one of some about at this point), apart from any investment dividends and market-based movements in asset prices.
4. You start a Roth pipeline during the first full tax year with only one income.
5. Keep going as a five-figure, one-income family for about 5 years. Then assess the situation and FIRE if you can.
At that point, about nine years from the present, if we assume average market returns instead of a flat investment environment, you'll probably have $1.5m+ in retirement savings, a paid-off house (or enough equity to relocate to a fully owned house), and hopefully a lot more clarity on the future prospects of your special-needs child.
There are also 72t / SEPP withdrawals which you can take from tax-deductible retirement accounts which allow you to avoid the 10% penalty on early withdrawals. They are discussed elsewhere on the forum. But I wouldn't counsel going straight to those in your circumstances. There have been family and friends of mine who have had special needs children, so I know up-close how much more complicated life can then become. For that reason I urge an bit of extra conservatism. Perhaps at the end of 9 years, when Step 5 is complete, you will be in a position to set up SEPP withdrawals.
Good luck!