Bed wetting for children of this age is not altogether that uncommon with 5 to 7 million kids doing it. It happens for a variety of reasons. Here is information on this https://www.webmd.com/children/features/bedwetting-causes#1. patience is key. Best of health to you and all of your children.
If I was you I would put him in Napies until he stops
Wetting during the night is not uncommen for a 7 year old------ during the day is another thing. I would change doctors and try to discover why this is happening. Good luck.
My grandson is 7 years old and is doing the same thing as your child. My daughter is very frustrated. We have taken him to the doctor and they say nothing is wrong. We need help because now the school is saying he smells and the children don't want to sit by him. I put him on a pull up this morning, put another one in his book bag and some underwear for him to change. I just don't understand. We need help very bad.
First of all, I commend you for your decision to help a foster child. That is a beautiful thing and takes special people to do it. This child has probably been through a lot in life for his 7 years if he is in foster care. You seem like outstanding people to go to the lengths you have to support and help him. It is certainly frustrating that he is urinating occasionally like this---- even though it sounds fairly infrequent. I would still continue with the watch (cool idea!) and the verbal reminders and keep at it. As the nighttime wetting is still going on (which is not uncommon to go on until 8 or 9 for sound sleepers) and this occasional wetting, I would also mention it to his physician at the next visit. He very well may not get super strong signals that he has to go. I'm sure that he does not enjoy urinating on himself and feels bad on the inside when it happens. Perhaps work with him to stop the pee if he forgets to go and then RUN to the bathroom. Then the damage would be more minimal. He'd have to change his underwear and pants---- but furniture would be saved. My 4 and 5 year old will occasionally forget for a second and a little dribble of pee comes out and then they shout----- I HAVE TO GO POTTY!!!!! and we all get out of their way as they race to finish the job. If they all out just pee--- it is a much bigger mess. Good luck and many blessings to you for the kindness and love you are showing this boy.