It is way too expensive to overdose on LSD. Estimates of lethal doses of LSD are much higher than 20 mg (20,000 ug) administered orally, more than 200 times a normal moderate dose of LSD (100 ug). The administration of this amount would require the ingestion of more than 200-400 units of street blotter, which typically contain about 50-100 ug of LSD.
Let me say this loud and clear- nobody has overdosed on LSD. There exist dangers with the substance in question, but overdose is not one of them. Let's educate our children with truth and honesty. Psychoactive substances are not for kids.