The youngest I have been to a funeral for was my nephew who was 14 months old. That was 7 years ago.
It was hard on so many different levels. But we were/are strong for each other as family.
My SIL has never been able to go to his gravesite. My brother does go occasionally, the live out of state now, and when he is in town and can get away from his wife and daughters he does go. My mom and I are pretty much the only ones that go though.
It is hard but faith will get you and the family through this. It won't be easy though.
Less than 2 weeks ago we also attended the funeral for a 19 year old. My DH commented to me then, he said his preacher dad always told him, when you see a really long procession, you know it's a child. Older people out live so many of their friends. But when it's a child, everyone always attends.