In order to sum up the above comments, the corresponding books for these nick names are
1. Baby = Principles of Mathematical Analysis;
2. Papa/Big = Real and Complex Analysis;
3. Grandpa = Functional Analysis;
and it seems that the difficulty of contents of the books grows with the age of the nick names! Firstly, you are a baby and things are easy to handle. Then you grow up and become a papa and things get more complicated. Finally, when you are a grandpa you should take care of your legacy very carefully which needs a hardwork! So 1 is a prerequisite of 2 and 2 is prerequisite of 3.