As others have said, there isn't a walker or mountaineer who hasn't ever made a navigation error - we have all done it and often. As we get more experienced, hopefully they are less frequent and more minor in nature, but we still make them! Even with a GPS, if you look at some unedited GPX tracks you will often see short (or sometimes much longer!) "spurs" where the walker has overshot their turning by some margin, then realised and returned the same way to the junction to proceed on the correct path. My GPX tracks have them from time to time when I have been chatting or not concentrating!
There is a lot of good advice here generally centred on being able to read the map so you can interpret the landscape around you and answer the mental question - what do I expect to see/find next? The SMC Navigator's Dozen mentioned above is a great place to start. Map and compass skills are the answer to the question of what will I do if (when - as it will at some time) my phone dies mid-walk?
OS also have some very useful material on navigation and map reading here:
https://getoutside.ordnancesurvey.co.uk/guides/beginners-guides-map-reading/ Navigation is a life skill.
While you are developing your map reading skills, if you are using a phone app (or outdoor GPS receiver), as forgotmyoldpassword said it is a good idea to plot where you expect to be going on your walk and load this GPX route into your phone (or GPSr). This image shows the 1-25,000 Ordnance Survey (OS) map with your section of the YWW plotted in red. One it is so much easier to see as it leads your eye right to it and two, if you do overshoot a junction you can very quickly decide whether to retrace your steps or make a detour to re-join the route further along. If your GPS position is not on the red line, you are off-route and can quickly workout why. The following two images I hope make this clear.
If you don't have the particular OS map sheet, you can easily print a section out, overlaid with your route. It is not expensive to get "proper" OS mapping on your computer and phone - at £24/year, the OS Mapping app is a steal and you can put it on your son's phone free as well. Just don't forget to download the mapping you need for your route before you go.
Open Source mapping is usually less detailed and having the route plotted is an even bigger advantage as this image of the same section of Open TopoMap (not as clear as the mapping you shared with us):
A few more suggestions. Definitely "practice makes perfect". Share the navigation with your son taking turns (print out two copies of your map section). Given sons generally like tech, see if you can get him involved with digital mapping, check out route-sharing sites and see if he can find the "best" walk in your area where he'd like to take you. Get him plotting the GPX track, and look at the same track on Google Earth in both 2D and 3D views. Take a look at the
Geograph site where every 1 km square of Great Britain and Ireland has a set of photographs (you can add yours too!) it is amazing what interesting things people have photographed. I also use the
Historic England site to see what scheduled buildings, battlefields, monuments, standing stones, rock carvings, parks, gardens, shipwrecks and more might be located nearby to add interest to a walk.