Survivor benefits for children

In general, children under age 18 (19 if still in elementary or secondary school) or disabled receive 75 percent of the deceased worker's benefit amount.

However, there is a maximum amount per month that can be paid to all the survivors on the record. The limit varies, but it is generally equal to about 150 to 180 percent of the basic benefit rate.

So in your case, the elder child (in college) will likely no longer be eligible, but since the two children were at or below the family maximum, the benefit to the younger child will likely NOT increase.

References :

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