What Mouse says - there are benefits to your DP of having you be a SAHM.
I actually took redundancy just over a year ago, as I was desperate to quit a role I used to love for a number of reasons and the pay offer made it a no-brainer for me (2 years pay).
I've done some cool stuff, sorted out a lot of support for ds, done a little work but concluded I don't want to be self-employed, and now looking for work. Which is taking longer than I thought it would, as applying in my field is so onerous it's hard to do more than one application a week. But if I just needed money I could get temp work at a lower level fairly easily.
Do you plan another child? If not, fees will go down hugely in two years. If so, may be worth sticking it out to get more savings and childcare vouchers. (took me over 8 years to get pregnant with ds, but then knocked back the Clomid and it worked on the second go).
If you could cope on one of your wages, then taking the deal sounds like a good idea - and devote a month of your time out to seeing if you can overpay mortgage but get back if needed, ensuring all insurances and wills are in place, utilities are on the best deals, etc. Life as a SAHM can be a lot cheaper as you can shop around more, get reduced items, not pay for commuting, etc.