There are three things you can do to sort children into their birth order in charts and reports:
1. Upgrade to the current version of Legacy Family Tree which has automatic sorting of children as they are added. To set the option, click on Options > 2. Data Entry and go to 2.2 When Adding New Spouses, Children, and Events. Next select the sorting options you want and click Save.
2. You can globally sort all the children in your family file in Legacy by clicking on Tools > Other Tools > Sort Child, Marriage, and Event Lists.... Next check mark the lists you want and click Sort the Selected List.
3. If you do not want to upgrade to the current version of Legacy, create a Potential Problems List that contains only searches for children listed out of birth order. You can sort the birth order right in the Potential Problems List. Here's how:
Click on Reports on the menu bar, then select All Reports (Books and others) and click the Potential Problems button.
Clear all of the check-marks from the Warnings, Problems, Standardization and LDS tabs, with the following single exception. On the Warnings tab leave checked the box for Check sort order of children.
Click the Create Problems List button.
Going line by line, click the Edit Children button on the right side of the list.
In the Children screen click the Sort button on the right side of the screen; then click OK and Close.