Is the smell of sharpie bad for kids?

Sharpies. Some people are very sensitive to it (same thing with perfumes, sprays, paints etc) . It can make them dizzy, short of breath, trigger asthma attack, even severe anaphylactic reaction. On your kid, it depends on what you observe. Use sharpies to write , not to smell it. If you kid have symptoms then consult with your doctor.
If they are huffing. It, yes. The incidental smell means a few molecules are getting in, but that is unlikely to do any harm. However, the solvents that are in sharpies are similar to those found in airplane glue, liquid paper and other volatile substances, and can cause a great deal of harm to the brain, liver, kidneys, heart and bone marrows of people who inhale or "huff" these substances.