I haven't got my NOW box to check at the moment.
But from the top line of the box main home screen where you see the gear wheel icon top right, what happens if you highlight and click on "Kids" from the top line.
Does it then take you to the kids screen with all the relevant kids channels or not ?
Or are some of the kids channels missing by following my instructions above?
Click on the accepted solution again or if that doesn't work click on the three vertical dots where there may be an option to undo the marked solution.
I checked on my NOW box by following my previous instructions and the kids section seems ok my end.
Perhaps try unplugging the power to the NOW box for a minute or if that doesn't work see if there is a software update available on the box.
If using a NOW Freeview Smart box with the blue NOW TV logo on the top casing, then try going to My Apps first on the LHS of the screen, then click on the NOW App then follow my instructions in my first post above.
From the accepted solution post, click on the three dot vertical button top right and then from the drop down option click on "not the solution".
See example from this screenshot below which just worked on a different thread which I originally started.
You could also try step 6 in this linked article below, just in case the software is corrupted.
Even if on the same software version number is the same has existing, update it anyway.
I just tried my NOW Freeview Smart box (assuming this is the NOW Box you have) though I don't use anymore and I found by clicking on My Apps on the left hand side of the screen, then clicking on the NOW App, then from the newer layout with the gear wheel icon showing top right corner of the NOW App screen, then on the same top line of the screen where you see "Kids" click OK on it and the screen should refresh into the kids section.
I don't use the kids section myself, but having a quick glance it looks like everything is there for me.