What you should do in this case is to divide one large square in four smaller ones. Then on the line above the upper left square put the letters 'IA'. Next, on the line above the upper right square write the letter 'i'. In the same way, on the left side of the upper left square write the letters 'IB' and under it, left from the bottom left square write the letter 'i'. This gives you something like a table. In each of the blank squares you connect the corresponding letters together, from the upper and the left side to see the possible genotypes of the children.
Meaning, their genotypes would be: 25% IAIB, 25% IAi, 25% IBi, and 25% ii
Hope this helps :)
