Firstly, congratulations to you for doing so well, and to your dh on getting another job.
It's always much more complicated than the simple maths isn't it? Of course there is the money side to it, but there's also your self-esteem and happiness, the complexity of your day-to-day lives, and the risk in this uncertain economic climate.
Is your dh concerned that your continued working will make his day-to-day life more complicated? will he have responsibilities for picking-up / drop-off, or might he have to take time off if the dc were sick? Did he enjoy you being a SAHM because it made his life easier? If so, what can you do to reassure him about his concerns and persude him of him equal responsibilites as a parent.
How did your dh feel as a SAHD? Does he feel that the traditional roles are now re-established, with him as wage-earner, and if so does that improve his self-esteem? Unfortuntely you have both experienced redundancy, perhaps he can be persuaded that employment for both of you reduces the overall risk of your household being without income in the future (or perhaps this is an idea that he doesn't even want to consider?)
As for you - the benefits are many - a feeling that you are contributing to the household income, you are working and getting experience and access to opportunities. How long till your youngest dc is at school? Can your dh see this in terms of a longer time frame?
Also, the cost of childcare should be something joint, it is not solely your responsibility i.e. coming from your salary. In fact, you could argue that since you have been working and supporting the family and HE is the one who is now going back to work, then the cost of child care should be deducted from his perceived income.