I have found the manifest for the trip Ellen and the children made from Ireland (via Liverpool) with arrived in Philadelphia in 14 April 1847. They travelled on the ship Arabella - Ellen, Patrick, John, Thaddeus Jr. , Peter, Mary and Michael (infant). The image is available on Ancestry.com.
The father, Timothy Thaddeus Sr., is not shown on the ship's manifest - I assume he traveled to the United States earlier. Some others in my family sent one individual across first to get things settled/arranged. Additionally, Ellen was traveling with a very young infant (noted as born earlier in 1847); it's possible they choose to have her depart later so she could travel after the birth...? GIven that they had a baby that young, it would seem the earliest Timothy Sr. could have come over was sometime in 1846. I've not been able to locate him on a manifest yet.
Timothy and Ellen are my Great-Great-Great-Grandparents. :)