https://www.naselin.com/blogs/is-nasal-spray-safe-for-kids-heres-what-you-need-to-know
I'm unsure if nasal spray for hygiene is good for sinus as opposed to teaching children to blow their nose.....but I suppose it helps to stop picking in public!!
The problem is that allergies cause sinuses to become swollen. It makes it difficult to blow your nose because the narrowed passageway prevents them from draining properly. Pretty common with allergies. When I was a kid, sinus congestion hit me pretty badly. Standing up, I was okay, but when I laid down, breathing soon became extremely difficult because it wouldn't drain. I was never able to mouth breathe when I slept.
Without Oxymetazoline Hydrochloride nose spray (Afrin and other brands), there were times I could not breathe and sleep. Nose spray is a vasoconstrictor that makes sinus tissue less swollen. (It also helps stop nosebleeds.) As an adult, I found I had little need for nose spray except once in a while in high allergy season.
Antihistamines are problematic. Most put you to sleep, so you see them in OTC sleeping pills. You may not sleep well. They leave me groggy in the morning and much of the next day. It can take a couple of hours to kick in fully. Non-drowsy antihistamines are less effective. Oral decongestants keep you awake and raise your blood pressure. Nose spray works immediately. If you feel more than a slight burn, you've overdone it.
Nose spray is not recommended for kids under six because they've never been tested that young. Given the expense of doing so, they probably never will.
Like any medicine, use it sparingly, and you'll be okay. The problem is that your body can come to expect it. Use it daily, and It loses effectiveness, and you'll eventually experience rebound congestion. Three days is about the limit. Use it once in a while, and there's no problem.