If I had kids and they were in diapers.
I would embarrass them by checking their diapers in public or when around family etc and would check the diaper without any notice.
I would also change their diaper in public or whenever others were around.
When it's warm or when they are inside the house they would wear just diapers, shirt and socks or sometimes just the diaper.
They would also go out in public with just diaper, shirt and shoes so the diaper would be noticeable and I could check their diaper easier too.
That is unless it's cold out then of course they would have clothes over the diaper.
I would also carry a diaper bag and ask them if they are wet or poopy and in need of a change.