Gentle giant with my children

My children were four and six when we got our Mastiff puppy. He is now three and bigger than both of them. He has been gentle, patient, and protective of them from the beginning. He lies down when they approach to bring himself to their level. He lets them climb on him. He watches over them in the garden. He is the most devoted guardian I could have asked for and the gentlest companion my children have ever had.