What do you say to the 7 yr old sister of a 2yr old boy who has been d by their father?

That is a terrible tragic story and I am so sorry, only God's love will help restore this situation, sometimes we don't understand why people do the things they do, I would contact a pastor or priest someone like that, maybe a counselor used to dealing with those types of situations, you will need professionals to help, and just lean on the Lord for strength and guidence, God can help take the pain away by taking it out of our minds so that we don't think about it or dwell on it, My prayers are with you and the whole family, May God Bless!!