Hi Bossbaby12 Where there is a will, there is a way.
I have a 21m DC and currently 6 months pregnant. I did worry initially about money - but my desire for 2 DC over took this.
Currently, I work 4 days a week, DS goes to nursery 3 days a week, The 1 day I'm working and he isn't at nursery - I either work from home or my mum has him.
When this baby is born, He'll still go to nursery, but only 2-3 half days. Like you, I want DS to continue to have the interaction with other children - but we definitely couldn't afford for him to go full time. And I'll be home, so it makes sense for me to have him home with the baby & I too.
When I go back to work after Maternity, DS will be just turned 3 and will be entitled to 30 hours a week. So, at this point, we'll be paying the bulk of fees for the new baby.
I'd say look at the non-vitals in your expenditures and see what you can cut back on. Mat Pay is rubbish, but your work may offer a little more and see what you can start saving to make mat leave a little easier for you.
Like i said - Where there is a will, there is a way!
Good luck with what you decide to do x