Some children light up when a room sings to them. Others visibly shrink. Both reactions are normal, and only one of them gets planned for by default.
The candles and the song are a tradition, not a requirement. Skipping the sung moment entirely, or doing it quietly with only the family present before guests arrive, is a complete option, not a compromise.
Telling a child in advance exactly what is about to happen, and giving them one thing to do with their hands and eyes — blow out the candles, look at the cake, not the room — gets most children through a moment they would otherwise dread.
Some children find the moment far easier standing next to someone else, or holding a pet or a favourite toy in front of them. It does not need to be endured alone to count.
No. Plenty of families do it quietly or skip it, and the child still has a full, happy birthday. The cake and the day matter far more than the song.
A guest expecting a tradition does not outrank a child who is genuinely distressed by it. A short, cheerful "they would rather skip the singing" handles it completely.
Part of our guide to Filling the unstructured days.