My daughter has a cavity and she is 3 years old her pediatric dentist says she might need laughing gas to relax her is that safe for her age?

Yes if: It's safe for any age if administered properly by a licensed practitioner. That may or may not be sufficient for a pediatric dentist to get enough cooperation with a 3 year old in order to do whatever dental treatment is required. Some pedodontists are amazing at treating children, even at this early age. However, some children require more and need general anesthesia in a hospital setting.

Vocal anesthesia: Always try to allay any fears in young patients as well as older ones by talking and showing what you are going to do.Sometimes a child will let you drill without a needle but if the child is too afraid than nitrous oxide (laughing gas) is indicated with a trained professional.

Nitrous for a 3 yo: Good luck coaxing a 3 year old to "breathe through her nose" (remember, dentist is working in her mouth!) to "relax" her. The safety comes from the current competence and training of the dentist, regardless of the age of the patient.

Yes: Pediatric dentists are skilled in anesthesia for children. Better your 3 year old should be comfortable and not mind the experience. That's why you see a pediatric dental specialist.

Nytrous Oxyde: There are dental offices where a 3-weeks course-trained-dentist/ "anesthesiologist" will provide general anesthesia to a 3 years old. And there are plenty of dental offices in a pediatric hospital setting staffed with real pediatric anesthesiologists and where the dentist is performing the job he has the most training for. Which setting do you think would have the least complications?

I would be : More comfortable giving general anesthesia to a 3 yr old in a hospital setting with a dedicated pediatric anesthesiologist. My main concern would be loss of airway and aspiration.

Yes: Yes it is. Kids have a higher risk of having a "bad trip" from it though. If it happens don't be alarmed its normal it'll go away.