Two too many

I have taken on the task of taking care of two more kids. I have been looking for another source of income for Dave and I and for the last several weeks, I have been posting on craigslist for childcare jobs. I have received a lot of hits but nothing has ever gone through until this week. A mom needs me to take care of her two boys, ages 3 years and 5 months. It is only 2-3 days per week for 6 hours a day. Today is my first day and I am feeling completely overwhelmed. I am not sure what I was thinking getting into this situation but right now I feel I am in way over my head. The 5 month old, Reed, took forever to get to sleep this morning and he screamed and cried for what seemed like hours. In all reality, it was only about half an hour but during that time, Emily and Blake (3 years old) were hugging and fell down. Emily banged her head on the garage floor and began to cry. I had my arm full of crying babies and then Blake started to cry. I am not really sure how but I was able to get everyone inside and taken care of. I was finally able to get Reed to sleep and he has been napping ever since but Emily and Blake have hurt each other several times. They are not purposefully hurting one another, but they are both so wild and crazy that it keeps happening. They also keep running around the house yelling, which is great because they are toddlers and that is what toddlers do, but there are sleeping babies in the house. I try to keep them centralized in the living room, farthest from the babies, but they keep running off. I am not sure how Reed has stayed asleep. I keep going in to make sure he is still breathing. By some miracle, all of the kids are sleeping right now. I am trying to decide if this is what I want to do. When things are going smoothly and all of the babies are happy, it is a lot of fun, but that is really rare. On top of all this, I feel the mom is taking advantage of me. She persuaded me bellow my asking price and told me it would only be for 6 hours. This morning, she showed up half an hour late (I can understand this, having kids and all, but give me a call already) and then when I asked her when she would be back (which should have been 2, she said 4:30). I didn't say anything to her at the moment, but I think I will be talking to her when she gets back. The money is definitely not worth what she is asking for. Her kids are cute and fun but it is a lot of work. I also feel bad because at times I feel I have to neglect my own kids to take care of the other two.
Some highlights of the day have been:
Reading to the older kids
Watching the rain
Jumping on the air mattress
Eating Sponge Bob mac&cheese

Here is a picture of Emily and Blake on the air mattress. They are already good friends!