The majority of bites and stings from spiders and insects are not poisonous and require minimal treatment. If your toddler is bitten by a spider or stung by an insect, you should clean the area with soapy water. If the area is swollen or red, you can apply ice wrapped in a cloth. Paracetamol or ibuprofen can be given for pain associated with a spider bite.
If your toddler is bitten by a poisonous spider such as a black widow, or if he is stung by a poisonous insect such as a scorpion, you should get medical attention immediately. If you are able to capture or kill the spider or insect and bring it with you to the emergency room, it will allow the doctors to identify it so that they can better treat your child.
If you notice a bite or sting on your toddler, but you did not see what caused it, you should treat it as you would a minor bite or sting. Naturally, if your toddler is in severe pain or having other serious side effects like trouble breathing, you must get medical attention right away.
With any bite or sting, you need to monitor it for a few days just to make sure there is not an adverse reaction or infection.