Hello, my 3 year old son sometimes has spit bubbles come out of his mouth while sleeping. i used to think it was foam but i can see the spit bubbles now. he does this usually when hes trying to breathe out of his nose while he has a stuffy nose, but i wanted to know if this was normal. thank you !
I feel your concern is due to nose block as you have mentioned and when free air movement is restricted it would cause saliva to form bless like how child Chat Doctor.  In my clinic I would give medicines to relieve cold and ask you to make him sleep on a side and observe. You could discuss with your doctor for personal examination and help