it depends on the age of the child but personally filling require drilling first and this can be painful. lidocaine injections can anesthetize the area of the tooth and make the procedure virtually painless however the needle does have a brief "pinch" that adults tolerate but kids may not. nitrous oxide (laughing gas) can be used for brief procedures as long at the dentist has the skill and expertise in doing this type of sedation/anesthesia in children.
do you need laughing gas or needles when giving fill-ins for cavities to a child?