My 2nd child had this. The specialist said to monitor it and check it again in 6 months time. He said a lot of kids 會自然好. If it doesn't, we can then consider having grommets inserted into his ears to help drain the fluid.
I felt very guilty - my son never complained of pain in his ear, so we only found out by accident that he had this condition. I thought he was just being naughty with all the shouting and loud TV, or that he was just ignoring me when I called him.
A month later my son was diagnosed with 睡眠窒息症. So the specialist decided to perform surgery - tonsillectomy, adenoidectomy - remove both the tonsil and adenoids. He also decided to insert grommets - the risk before was putting a young child (4yr) under general anesthetic, but now that my son need to have surgery anyway...
Result of having grommets was to be extra careful when shower/bath/swimming - to avoid getting water in there. So we purchased special ear plugs, and swimming caps.