@NCperson
State benefits may very well be affected by the other support available to the recipient, such as, do they live with someone who provides for them, and what is that person's income. Only someone familiar with the rules of this particular program in this state could answer, although I would try to find a social worker to talk to before I called the state agency itself.
@msong06
The tax laws do allow you to claim your child as a dependent if the child lives in your home more than half the year (or more than half the time since their birth, if they were born during the year). Claiming your child would give you up to a $2000 child tax credit, and may make you eligible for EIC, depending on your income. It would also make you eligible to file as head of household which has lower tax rates than filing as single.
You may also be able to claim your GF as a dependent, if she lives in your home the entire year, and you provide more than half her support, and she has less than $4700 of taxable income. Support provided by you includes a share of your rent or mortgage, utilities, food, and other housing expenses. (A 1/3 share if there are three people in the home.) If she receives support from the state, such as SNAP, welfare, food stamps, medical insurance, or other benefits, or money from family, friends, church, etc., that counts as support not provided by you, and you have to add up all the support to see if you provide more than half. However, benefits provided to her child don't count as benefits provided to her. Claiming her as a dependent would qualify you for a $500 credit but does not increase your EIC.
However, we can't tell you about the rules for Medi-Cal, and whether your support will affect the benefits she or her child gets. If you are hiding from Medi-Cal that you are living together and supporting her and the child, then claiming them as dependents will disclose that support to the state (through your state tax return). However, I don't think putting it on the tax return will change anything if you have already disclosed to the state that you are helping to support them. But only an expert in Medi-Cal rules can tell you for sure.
