To put a picture on your profile you need to get an image with an image tag.
If you got on www.photobucket.com and register upload a picture and you will be provided with an image URL, TAG and IMG then copy and paste the relevant one into the space provided on this website.
Not sure about a 4 year old kid sorry
Or you can upload a picture directly on your computer.
If you go on your account on this webpage and then at the bottom click on Change my Profile, down the side you should see Change My Personal Photo click on that and then upload your picture either using an image URL or directly from your computer