Cfg_InstInitialize : get all child products list

Hi,

I am trying to find a way to fetch all the child products and its attribute value and then using the details I would like to set an attribute with a value conditionally.

How to fetch the child product details which are already selected?

Scenario:

lets say the product structure is:

P1

>> C1

>>C2

>>C3

>>C4

to begin with, my customize screen has:

P1

>> C1 >>A1

>>C2 >>A2

Expectation:

I would like to Add A3 as the attribute value when P3 is selected (kind of sequencing).

P1

>>C1 >>A1

>>C2>>A2

>>C3>>A3