[Supay]

Yes this is because of the DB, I do remember someone else doing some changes to the views that are used for the kids to remove content. I
 can have a look at editing some of the SQL for you.

What are the 3 sources you want for the kids?

Thank you for this!  Though I imagine if you get a nice way to work this out you will also make a lot of others happy.  The sources I want specifically for the children are below.  I have them in folders based on UK age ratings for films and just a kids TV folder.

        <default pathversion="1"></default>
        <source>
            <name>movies-12</name>
            <path pathversion="1">nfs://10.17.42.50/srv/nfs/movies-12/</path>
            <allowsharing>true</allowsharing>
        </source>
        <source>
            <name>movies-pg</name>
            <path pathversion="1">nfs://10.17.42.50/srv/nfs/movies-pg/</path>
            <allowsharing>true</allowsharing>
        </source>
        <source>
            <name>tv-kids</name>
            <path pathversion="1">nfs://10.17.42.50/srv/nfs/tv-kids/</path>
            <allowsharing>true</allowsharing>

@Supay Sorry for the delay been away with work.
Give this a try

Kodi V119 - 05 Custom Views.sql

This is set to create the views for U02, you can change easy on line 12
at the bottom of each view I have added 3 where strings

sql:
  WHERE

    `path`.`strPath` LIKE '%movies-12%' OR

    `path`.`strPath` LIKE '%movies-pg%' OR

    `path`.`strPath` LIKE '%tv-kids%';

more can be added and even removed as long as there is a OR at the end of each line except the last line that needs a ;
the % is wildcards.

Let me know if you get the desired results.

If the string are found anywhere in the path it will show

Sorry for the long delay.  Life went a bit crazy and I wasn't able to do anything further to my systems since then.  However, sometime after you posted this (again not entirely sure when due to chaos here), all of the content in my kids profiles that I did not want them to see just vanished of its own accord.  It has remained that way since, they can only see the content that their sources provide and the adult profiles can see everything.  I have no idea why, as I made no changes to either Kodi or the database other than Kodi updates, but it now works exactly the way I wanted it to.  I'm unsure if this is simply part of an update to Kodi to provide this function more easily, or if there was some odd delay between the initial setup and my clients realising they should only be showing the added sources.  Whatever happened, it works and had no need for any changes by me.  I really appreciate the information you provided though and if I find out anything further as to why this just started working I will reply again.