I suggest asking yourself, if I don't make it to OS, will I be happy being a general/ paediatric dentist?
If I don't make it to OMFS will I be happy being a doctor in a different area of Paeds?
Maybe this job exists, but it will be rare, and to get to that level of sub-specialisation will take at least 2 more years beyond 3 year OS specialty training, which is itself highly competitive (as is Paediatric Dentistry). So I advise you research exactly what Oral Surgeons (Dentistry plus 5-7+ yrs) and OMFS (need both Dent+ Med, plus core training, then 5+yrs) do. Certainly contact the BAOS. And check the Paediatric dentistry and Special Care Dentistry specialties.
By 'nitty gritty' do you mean things like Cleft cases (in my area the repair surgery is carried out by OMFS -'maxfax'- and simple cases sometimes assisted by staff grade OS - Oral Surgery- dentists ), facial tumours (can be OMFS/OS/ ENT/ combination) , Orthognathic surgery (OMFS)? Orthodontics, restorative and labs for prostheses are heavily involved in all these cases.
If you do, you are almost certainly looking at OMFS. Apart from in children's hospitals, you will see kids as part of your general caseload, or work as part of a multi-disciplinary team. Look at the GOSH site for example, and you will see that the surgeons are OMFS trained, working with dental specialists in paeds, orthodontics, restorative.
Edited to clarify that the Paeds GA lists mentioned above by Toothysmile do not usually necessitate Oral Surgery but are usually for simple multiple extractions of deciduous teeth or occasional first (less commonly second) molars. In England anyway, those lists are usually done by Community or Paediatric dentists with MaxFax called very rarely indeed, maybe for a fistula repair or very complex wisdom tooth.
Quite a few dual qualified aspiring OMFS people end up in a different medical specialty or stay in dentistry when they find the bit that they enjoy best.
Good luck with your decision.