Hopefully they have looked for and found child care that is in synch with the school year, so that they are paying for it 10 months of the year, rather than 12 (given a typical teacher's two-month summer break).
If ShanghaiStashing is right and her job is actually costing them money (or having them break even), then I automatically jump to the solution that she quit her job. That may be the right move for some mustachian couples, but often not a wise move for women (or couples) who don't think through the long-term impacts (both financial and non-financial) including the vulnerability that can ensue for the non-working partner. If the relationship goes sour, it would be much more difficult to leave if one had been outside the work force. For mustachian couples who are interested in digging deep into the workings of their personal finances and understanding their core values and only spending in synch with those values, having one partner not work outside the home, especially when there are young children, might turn out to be the best solution. For most other couples, there are many reasons to caution against this, including the financial and emotional vulnerability that could ensue for the partner no longer in the work force.
If they were actually interested in reducing their expenses, then they could look into various aspects related to her job, including her commuting (maybe she could car pool, bicycle to work or use public transportation?), not to mention whether they've just got way more car than they need!
Two observations: The Wealthy Barber, David Chilton, likes to point to teachers as being the most frugal professional group he knows. She may have a lot of opportunities for reducing expenses if she talked with colleagues about their expenses and how they make their households work on what I would guess is a lot less money in most cases.
This couple is the same age (give or take a couple of years) as Mr and Mrs MM!