Alexa is right. It could be teething problems. They have a very strong urge to bite anything.

Also don't make a big fuss out of children doing these things. They will think it is fun and will do it again and again. Just ignore it and things will change quickly. You don't have to spank a 13-month-old child to change it's behaviour.

"Life is like a bicycle, if it's too easy - you're probably going down :)"