*Slow cookers a great idea.
*Wash your 'whites' or your 'darks' the night before, that way, first thing in the morning you can hang it out.
*Bath your son and your DD at the same time....baby will be fine on the floor for 2 mins whilst you dry, dress your son.
*The days your son is at preschool, do a farily big household task i.e clean the shower, mop the floor, or dust the house. Doing just ONE of these things is a major achievement in itself with two little ones...
*I often mop the floors, or fold the washing at night, when the little ones are in bed. Whilst my mountain of washing looks daunting in the day, at night you will be surprised how quickly you can fold it and put it away with no interruptions.

Good luck, i was soo nervous the day my DH went back to work when i had my second.
I promise, in a few weeks you will be in the full swing of it....and doing just fine....