The only way to go, in my opinion (was referenced by someone else, too), is the NeilMed sinus rinse bottle. No tipping and pouring - this has a straw that goes to the bottom. There is a pediatric size, but I'm not sure for how young. MUCH better than anything else.
So here's the trick (taught to us by a National Jewish nurse):
-mix the solution packet into the bottle with lukewarm water
-get out the kleenex and lean over the sink
-put the bottle up to your nostril and "blow out the candles" - blow pretty hard - literally like you would to blow out candles on a cake WHILE YOU
-squeeze the bottle gently and let the solution run out the other side of your nose
- blow your nose
-do half the bottle, repeat on the other side.
And to those afraid of doing it? I was terrified, but made myself. If my son could do it every day, sometimes twice a day, I had to see how it was for him.
Also, nasal sprays don't do anything like this - they moisturize, but will not rinse everything out. Trust me - it's not always pretty.
My son has no allergies, but nonallergic rhinitis. He was never able to breathe through his nose until we started using this - every evening (at least one hour b/f bed) when healthy, twice a day when not. Can't even begin to tell you how much it has helped him.
Hope this helps!