Modifies fm_yaml and field_manager to eliminate references to children

[GFDL-Eric]

Description Include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

How Has This Been Tested? Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration (e.g. compiler, OS). Include enough information so someone can reproduce your tests.

Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] Any dependent changes have been merged and published in downstream modules
• [ ] New check tests, if applicable, are included
• [ ] make distcheck passes

[rem1776]

Closing since this will get replaced by @J-Lentz's PR