It will take 16 days.
We first find the rate that each child eats eggs at. 30 eggs in 12 days = 30/12 = 5/2 for all 8 children. Dividing this by 8 to find the rate per child,
5/2 ÷ 8/1 = 5/2 × 1/8 = 5/16
Multiply this rate per child by the number of children: 5/16(6) = 30/16
30 eggs would be eaten in 16 days.