I am not back full time but I work 4 days a week and to be honest this is more than 40 hrs most weeks...i agree with the tips above and would add a few things
I often cook food for DS on a Sunday so I havea back up of food for him for the week, I provide his food at day care so need lunches etc as well as dinners etc.
I also have an arrangement with a friend with a baby the same age (who also works) and when we cook up a batch of food we give a few serves to each other, just to add to variety for the kids. this works really well - keep them in the freezer.
i often cook double so DS can have some of our dinner for lunch or we can have as left overs
I have a range of easy meals i can make in under 30 mins for dh and i
we have just started having alternative 'nights off' - ie one does the night routine bath/bottle/bed - we used to do this together... this gives 20 mins of 'down time' or one of us can go out or to gym or whatever without having to be there for bed time ever single night - this was bc i was struggling with no time for myself
obe of us drops off and one of us picks up from care each day usually

good luck - i find the guilt i feel is a lot worse than the reality for DS
xxx