Hello Mosquito repellent contains pyrethrin compound.When consumed in toxic dose it can cause mild to severe toxicity depending on the dose and body metabolism. The symptoms may be mild nausea,vomiting,abnormal movement of body,increased salivation,respiratory distress and even respiratory failure and coma. As your child has not consumed the liquid and just chewed the stem,chances of toxicity are less.But as i said it depends on body metabolism and metabolism of every child is different,be careful for the symptoms I mentioned above. Once there is toxic symptoms only washing of mouth and giving plenty of fluids is not sufficient.One should consult emergency room for proper assessment and management if needed like gastric lavage,inj atropin,IV fluids etc. I would suggest you to be careful for any abnormal symptoms and if there is any consult emergency medical room immediately. Regards