Since you say you are newly separated, I would think that this may be affecting your 5 year old. I know it's extra work, but I'd get a plastic liner or puppy pads, and put under the sheet on the bed, so that accidents aren't such a big deal. The hiding pjs worries me a bit as it tells me that your little one is ashamed of wetting the bed - which unfortunately exacerbates the problem by adding more pressure to them.
If this one sleeps well, maybe wake the when you go to bed to "try" to go - most will react positively to the cold toilet seat and go back to sleep afterwards very easily. Talk to your child to see what's worrying them and make sure they know you aren't upset at them for peeing the bed. Ask them not to hide their pj's, just t put them in the laundry basket and let you know. Make it matter of fact, no big deal.
It may be a reaction to something that's happened at school on that particular day, it could be that the child is just sleeping really soundly.
My one granddaughter had accidents until she was about 8 or 9. My daughter tried all of the above, and then when there was a depends ad on tv one time, Angelica said, "that's what I need for bedtime" and my daughter bought her some large pull-ups. Didn't need them for long, once the worry about wetting was gone, so was the wetting.
Good luck though, I know it's frustrating and hard with the extra laundry.
With your 2 year old, we always made a big deal of nanny/mummy making a tinkling sound in the toilet, and then asking the little one to do the same. Then we always flushed and waved "bye bye" to the pan as it flushed, LOL
Hope this helps
R.:)