Yesterday, I collected my niece (almost 13) from a full fare carrier, after long haul (SAA into LHR). She said that they did look after her at both ends and all the way through to airside. Although I did not notice the person, she said that they were right behind her as she came through the doors.
OK, this was long haul but I would be very anxious with anything less than being accompanied by the carrier.
If you cannot make the return trip, perhaps, get a trusted member of your family to spend a day reading a book whilst making the journey? As you say, still cheaper than paying full carrier cost.
I think my concern is for when things go wrong. If the flight is delayed or re-routed. Someone who can wield a credit card and make awkward decisions? If they are with a full service airline then you will get all of that and relays of information on the delay. If you are a small family, or they live far away, perhaps a 'god parent' of the child would like to help out as in loco parentis for 24 hours?
Out of interest and feed back to the rest of the forum, please let us know your decision and the outcome, as this is a subject that we have not had here for (I think) the last two years, at least. Thanks.