Adenoids and tonsils form part of the Waldeyer's Ring of Lymphoid Tissue and are the primary immune defence during infancy, where infants crawl and tend to mouth everything. They begin to shrink and disappear by 4th year of life and by 5 years should have completely disappeared. Tonsils take a bit longer to regress and by age 12 years they too become vestigial.
Next Steps
If I see adenoid obstruction in nasopharynx, in a child above years, I has to go! I usually post for LASER or COBLATION assisted Adenotonsillar Ablation. However, if the tonsils shrink 24 hours subsequent to administration of preoperative intravenous antibiotics, I proceed only to remove adenoids.