no.
That is ridiculous. Your child is on a crazy amount of medication, the doctor obvoisly does not know what he/she is doing. Sedation is ruining this kid's childhood.
Try just the Metadate for a week. ADHD is not treated with Seroquel. Seroquel is an anti-psychotic with strong sedative properties that makes the child appear to be calm. Seroquel is also only FDA approved for patients over the age of 18 for Bipolar mania and Schizophrenia.
In other words, your doctor is a quack, and that is not safe.
This is malpractice.
------------------------------------------------As an amendment to this answer I'll usually be quick to defend the recommendations of a doctor but I've only seen 200-300mg of seroquel given to patients who are in need of a strong antipsychotic. In fact in the normal treatment of bipolar mania I believe it's usually given out in doses of 25-100mg for adult males...so for a 5 year old child I would certainly say you're within rights to want a second opinion.