Benefit rates

The situation is not quite clear to me. However, for survivor benefits, a child under age 18 (19 if still in elementary or secondary school) typically would receive 75 percent of the deceased worker's benefit amount.

There's a limit to the amount that family members can receive each month. The limit varies, but it is generally equal to about 150 to 180 percent of the basic benefit rate.

If the sum of the benefits payable to family members is greater than this limit, the benefits will be reduced proportionately. (Any benefits paid to a surviving divorced spouse based on disability or age won't count toward this maximum amount.)

http://www.ssa.gov/survivorplan/ifyou5.htm
http://www.ssa.gov/survivorplan/ifyou6.htm