I was in a lawsuit settlement a drunk driver almost killed me when I was four. Since I was a minor it money was invested in Merrill Lynch. When of age and received small amounts of money at a time from them my family and I realized a lot of money went missing . How can I get that money back?

You may not, depends on how and why the money went missing, who was the guardian at the time, was the money used for your medical care.

Who took the money, out of the account, and why

A lawyer probably represented you in the lawsuit, so do you know who that is? What is your proof that money went missing, or your suspicions? Have the small payments stopped? Many many questions. If you can't pay for a lawyer now, contact Merrill Lynch and ask for a printed accounting going back to the beginning.

First step is to get an accounting from ML. Next step is to determine who was assigned as trustee and who had the power to determine what investments were made.

It certainly could be that bad investments were made reducing the amount of the settlement.

Where do I start?

Talk to an attorney. That is clearly the first thing to do.