Assuming that each child's allele is determined independently of their siblings, the probability of passing the "b" allele to any one child is 1/2.
So, the probability of passing the "b" allele to all four children is (1/2) x (1/2) x (1/2) x (1/2) = 1/16.
Therefore, the probability of giving the "b" allele to all four children is 1/16, or approximately 0.0625.