I am obviously not against praying, I think it is great. I think it would be wonderful to ask everyone to pray before leaving your own home, however in someone else's home, I feel like it is kind of stepping on toes and you giving an impression that you have some type of spiritual authority over that person. My Parents hardly ever have blessings on food or family prayer but I would never take it upon myself to lead everyone in prayer at my parents house. Because I would not want to undermine my dad's authority. I would just take my own kids aside and pray with them.