As others have said, you do not use a W-9 to file a tax return. But the fact that you were asked to fill out a form W-9 indicates (but is not 100% for sure) that you are working for some person, company or organization as a contract employee or independent contractor. You will probably receive a form 1099-Misc, in January or early February to document your pay for 2016. You do file with that. Such payments are classified as earned income and qualifies you for the child based refundable earned income credits.
So, yes, you will receive a refund. The money you hear about people getting for just filing a tax return claiming kids requires you to have some earned income (wages or self employment). With earned income, you are eligible for the "refundable" Earned Income Credit and the Additional Child Tax Credit. Contract employment is self employment, whether you receive a 1099-misc or not. So, keep good records of your payments and any expenses associated with this income.
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