Another strong vote for giving notice and ending this job.
And this part isn't what you asked or want to hear, but....as a mom who also gave up work to stay home, I want to add: Don't take on another babysitting gig, please. Stop looking for another child who might "fit your family" because there's no ideal child who is not going to create any "interruption to our flow" as you put it. And since any child you are babysitting for pay is going to end up getting your extra attention because you'll feel obliged to put that child first before your own in some ways -- Either find another way to make money or just stop until your kids are older.
If this is just for spending money (which you do say in the post) and not to meet bills, please reconsider. Your older child will be in kindergarten very soon, and your days of both kids with you will suddenly be over. Enjoy the time before K starts, and once K does start, you will have precious hours to spend alone with your younger child, giving the younger child some one on one time with mom that the second kid in most families seldom gets.
Unless this money is really for important reasons -- for the kids' college accounts, or to tuck away into retirement, or to help with essential monthly bills -- then I would drop the idea of paid work until both kids are in school. If you took time off working to stay home with your kids, then you and your husband figured out, before you quit, that it was financially OK to do so, right? Be confident in that choice and enjoy your kids before they are both away from you most of each day.
Once the kids are both in school (which will be in only two and a half years, which is no time at all) you can do work that will both get you out of the house and pay better. But your kids' young years before school will fly by; do you want to spend those years with someone else's kid in the mix if it's not truly necessary?