It’s not quite so easy without a camera, but there are various things you can try to see if there’s any activity in and out of the hog house. You could put some scrunched up paper in the doorway (or i.e. a flower, leaf or twig) where it would be moved if a hog exited, or if you have any you could try putting some sand in the doorway and just outside and see if there are any footsteps.
Sometimes the hoglets continue to use a hog house for a while after Mother hog has left them to go it alone, so make the object big enough that a hoglet couldn’t get out without moving it, but light enough that they would push it out the way.
It is more likely that Mother hog might abandon them when they are new borns. Once they are out and about she will have invested a lot in getting them to that size, so less likely to abandon them when they still need her. So I wouldn’t worry about putting something in the doorway disturbing them as long as you’re quiet.
The hoglets normally go out with Mum from about 4 weeks and by a couple of weeks later will be old enough to dispserse, so hopefully by October those ones will have left home (or Mother hog decided they are old enough to look after themselves). Then if the object hasn’t moved, I would still open up the lid carefully, but by that stage they shouldn’t mind too much if you are really quiet (if a hoglet does still happen to be there).
Meanwhile, enjoy watching the hoglets!