Being a caregiver is noble, but in most cases it won't earn you Social Security benefits. Caring for a sick father or a terminally ill girlfriend, for instance, doesn't entitle you to any benefits from the Social Security Administration. The exception is if you're married and taking care of your spouse's child. In that case, you may qualify for benefits of your own.
If the child you're caring for is 16 and receiving Social Security disability, you can apply for benefits. The most you can get would be payments equal to half your spouse's retirement benefit. You can keep getting benefits until the child turns 16. After that, even if he still receives disability, the SSA cuts you off. The exception is if you've turned 62, which entitles you to receive spousal benefits regardless of caregiving.
You can't apply for benefits based on age unless your spouse has filed to collect her own retirement. To get the full benefit -- half of what your spouse receives -- you have to wait until you reach full retirement age. The earlier you apply, the less you get, and being a caregiver, if the child is older than 16, doesn't affect that. Retirement age varies with your birth year: It's 66 for someone born between 1943 and 1954, then rises gradually to 67 for anyone born in 1960 or later.
If you're old enough to retire and also a caregiver, you don't get to double the spousal benefit. It may actually work the other way around: The total amount your family can get when only your spouse earned benefits is 150 to 180 percent of his retirement benefit. If your child has a disability income, and your spouse is retired, that probably uses up most of your family's allotment. It's your benefits that will be cut to keep the family under the limit.
If your own income entitles you file for benefits, they may be more or less than what you get as a spouse or a caregiver. If more, you don't double-dip: You get the benefits you've earned and nothing else. If less, the SSA will pay you enough spouse/caregiver benefits on top of your own that you don't lose anything. You can, however, postpone getting your own retirement benefits and settle for the spousal benefit for a few years. That boosts your benefits when you finally claim them.