Well if you are going to be paid your usual salary, I would offer to do some "light" housework such as laundry, ironing or even some dog-walking or vacuuming.
If you do not feel comfortable doing that, you can run some errands for the family.
Offer to go to the Supermarket, buy toiletries at Target/WalMart/Costco, pick up medicine at the pharmacy, mail packages at the post office, return books at the library, take the car for an oil change or car wash, and/or drop off-/pick-up any dry cleaning.
In any busy working household with a young child, trust me...There is ALWAYS something that needs to be done!!!!!