They don’t execute your kid for smoking pot.
“Any Singapore Citizen or Permanent Resident found to have abused drugs overseas will be treated as if he/she had abused drugs within Singapore. Consumption of a controlled drug is an offence and a person may face imprisonment of a minimum of 1 year and up to 10 years, or a fine not exceeding S$20,000 or both.”
You'll need to put more thought into it. Imagine your kid traveling somewhere, smoking pot, flying back to Singapore, getting randomly checked and facing consequences.