You need a will not just to leave money to your children but so the courts know who will take care of them should both you and your husband pass away at the same time.
So, yes you need a will. And you may have more to leave them than you think.
The the important point is that you aren't in a good financial position espcially with another baby on the way. This is very serious. If you are having trouble now, how will you make do with the extra baby and all the expenses that go with that.
You need a plan, a budget some intervention ASAP.
You can safeguard your children's futures by becoming very proactive in finding a way to boost your savings, get a will and hopefully some life insurance. Find out a financial class in your community. Go to www.debtadvice.org and set up a meeting with a nonprofit credit counselor. In addition to helping people with setting up debt repayment plans, the agency can help you and your husband manage your money better. If your husband won't go to the meeting, you go.
Please get help so your children are financially safe.