If you do clinical trials for half year and work the other half are the studies considered self employment or taxable income?

you file one return showing both

You will have to prove to the IRS that your participation in the trials rose to the level of a trade or business. While you claim that it is, I don't think the IRS will agree with you--especially when you have children and doing so increases your EIC/ACTC.

Both. They are self-employment and self-employment is taxable income.

They are taxable income, yes.

If you received a 1099 MISC for the trials, then it is taxable income. On the tax form there will be a place for listing any 1099 MISC forms. If you use a tax program, there will be point at which it will ask you for those forms. You enter all the information from them. Either the form or the program will then use that information in figuring out what taxes you own.

The number of dependents is usually listed at the top of your tax form or is input into your tax program. That information is then applied to all income listed on the tax form, whether you enter it from a W2 or from a 1099 MISC or other form. You do not have to do anything special about dependants for the 1099 MISC.

(Note: A copy of the 1099 MISC was send to the IRS at the same time the mailed a copy to you. They already have that information. So if you fail to list that income on you tax form, they will know and will come after you for it.)