Id have the table set up quite a bit differently
id | nav_name | nav_link | nav_parentid
Not sure what the nav_child is there for is that for the displayorder?
The parentid e.g. would be if its the main navigation link (section header) that its -1 else its the Section headers Id
an example
id | nav_name | nav_link | nav_parentid
1 | Test | /test | -1
2 | Test Cat 2 | /test2 | -1
3 | Link 1 | /link1 | 2
Link 1 would be in section Test Cat 2