Are healthy but large adenoids in a 4 year old expected to shrink enough in 1 or 2 years to avoid tonsil-adenoidectomy to treat mild osa?

Probably not: Tonsils, adenoids, and all other lymphatic tissue tends to enlarge until puberty, then begin to downsize. Ask pediatrician about referral for evaluation to an ear/nose/throat specialist. Note also that enlarged t&a can adversely affect cranio-facial growth. Go see orthodontist @ 7th b'day.

No: If the kid is snoring now at 4 things will just get worse.The tonsil/adenoild mass grows faster than the kid untill about 8, stabalizes and stops, while the kid grows bigger in adolescence. If the kid falls asleep during the day while his/her friends are playing, i'd have the t&a done over the summer.

Possibly: At birth, your tonsils and adenoids (t&a) are small and your immune system is immature. Your t&a are immunological structures and make antibodies to pathogens, like bacteria and viruses; so as you grow, they grow and enlarge, doing their job. Our immune system is relatively mature at 5 to 7 years of age, when the t&a peak in size. They then usually shrink to become small again by preteen/teenager.