How often should I let my child (a toddler) eat candy?

Ermmm as little as possible? Make it a treat when a child gets candy not a norm. Maybe they can get candy during their birthday, a special holiday, either on Saturday or Sunday. At such a young age, toddlers and too much candy often lead to all sorts of detrimental consequences -- tooth decay, obesity, sugar rush (I've seen this on my friend's toddler -- not fun AT ALL when the sugar high dies out).

Try to limit the candies intake among toddlers. Tooth decay is the biggest problem as they do not really know how to brush their teeth yet. There are many healthy snacks to consider for toddlers rather than candies, eg raisins, fruits

I let them eat 1 occasionally when their friends in CC give goodie bags on their birthday. Then my mil will secretly give the rest to the cleaners when the kids are not around. So the sweets just "poof" unknowingly. Lol.