In the Eligible Couple Registration Module, the system allows an age gap of only 1 month between the first child and second child, which is not biologically possible unless they are twins. There should be a minimum validation check of 9 months between the birth dates of the first and second child, unless they have the same birth date (twins).

Steps to Reproduce:

1. Navigate to the Eligible Couple Registration Module.
2. Register a first child with a birth date (e.g., 01-Jan-2024).
3. Register a second child with a birth date just one month later (e.g., 01-Feb-2024).
4. Observe that the system accepts the registration without any error message.

Expected Result:

• The system should not allow a second child to be registered with a birth date less than 9 months after the first child, unless they are twins.
• If an invalid age gap is entered, an error message should be displayed

Actual Result:

• The system accepts a one-month age gap, which is incorrect.
• No validation message is shown.