I try to have a routine...it doesnt always work out but if it's there you sort of know where you are, what you need to do and what you've acomplished iykwim.
My DC's are 3 1/2 and 13 months. Our days usually go something like this....
6.30am - 7am Get up with DC's
7am - 7.30 Breakfast. I'll tidy the kitchen while they're eating.
7.30 - 8am Get DC's washed and dressed
8 - 8.30 Get myself washed and dressed. Make DS's lunch.
Now try to put in load of washing. Unload/load dishwasher.
9am Take DS to preschool.
10am Get back. Have my breakfast.
10.30 - 11.30 Hang washing out. Mumsnet. Tidy round house. DD is usually quite happy to sit with toys etc.
11.30 Pick DS up from preschool
12.30 Get back. Give DD lunch and put down for nap.
12.30- 2.30 Play with DS. More tidying house...whatever needs doing the most! Ironing sometimes.
2.30 Get DD up from nap.
In the afternoon we do activities like painting, sticking, colouring etc.
I will do housework etc in between sorting the DC's out and as I go along.
4.30 - 5pm DC's tea time.
They will usually sit watching Cbeebies while I make tea for me and DP.
6pm - Bath
6.30 - DS milk and DD breastfeed
7pm - Bed
Our time outside the house is usually the mammoth walk to and from preschool everyday. We live in v rural place and so can walk through the woods etc on the way home. On the days DP isnt working some of the routine goes to pot but bedtime etc remains the same. On these days Dc go to softplay, swimming, aquariam etc.
To be fair to you your youngest DC is only 4 months so any kind of routine is a bonus. It's very difficult when they're so small but it does get easier as they get older!
Sorry for the essay!