You need to clear the decks, so get bin bags and do a couple of runs to the dump. Be ruthless throw out everything.
Open the windows to freshen up the place in general.
Get thick good quality rubber gloves, thick bleach, heavy duty paper towels, that blue stuff that comes on a roll is ideal, and lots and lots of hot water.
Bathroom--
Put bleach under the rim of the loo, round the top rim of the bath so it dribbles down, fill the sink with hot water and a bit of bleach. Dribble bleach on tiles on walls. Leave all of the above to get working while you-- Get a scourer and scourer the sink, any surfaces, taps etc. Get some paper towels and dampen, go round the skirting boards. De fluff. Now scrub your loo, your bath, tiles and then rinse. Lastly drain the sink, scour. Rinse. Use paper towel to shine everything. Vacuum then mop the floor. Will take you less than an hour.
Bedrooms. Be systematic. Gather up everything off the floor, dump on the bed. Vacuum the floor. Then put away clean clothes, make a laundry pile for dirty. Get baby wipes, and "dust". Make the bed. Job Done.
Living area. Go around the room with a empty laundry basket. Dump everything in there that does not belong. Vacuum, dust. Straighten up ornaments etc. Then go through the laundry basket putting everything away in the right place.
Matalan do 2 for £8 storage basket things in a variety of colours. Get a couple to dump toys in.
Kitchen--wash all the dishes, put them away. Put away everything you can. Fill the sink with bleachy water, as hot as you can stand it. Vacuum the hob top, and the oven. Get a couple of cloths in there, then lay damp on your hob, leave, go back to them in a few minutes, they will have lifted alot of the gunge off. Wipe all the surfaces down, then the cupboard fronts. Vacuum, then sweep then mop the floor with bleachy water.
Paint walls when the kids are in bed.