is normal for a 10 year old to look at dicks.

No its not normal he is way to young and the internet is a dangerous place for him to be unsupervised. You should install safe guards that block sites like those. If you care about your brother and his safety you will do just that. I would also explain to him about the dangers of internet and also explain what he saw as he may be confused or he may act out. It is your responsibility to protect him. Do so!!!!