See if this helps
DataTable person = new DataTable();
person.Columns.Add("Id");
person.Columns.Add("Name");
DataTable pet = new DataTable();
pet.Columns.Add("Id");
pet.Columns.Add("Name");
pet.Columns.Add("OwnerId");
DataSet ds = new DataSet();
ds.Tables.AddRange(new[] { person, pet });
ds.Relations.Add("PersonPet",person.Columns["Id"], pet.Columns["OwnerId"]);
DataRow p = person.NewRow();
p["Id"] = 1;
p["Name"] = "Peter";
person.Rows.Add(p);
p = person.NewRow();
p["Id"] = 2;
p["Name"] = "Alex";
person.Rows.Add(p);
p = pet.NewRow();
p["Id"] = 1;
p["Name"] = "Dog";
p["OwnerId"] = 1;
pet.Rows.Add(p);
p = pet.NewRow();
p["Id"] = 2;
p["Name"] = "Cat";
p["OwnerId"] = 2;
pet.Rows.Add(p);
foreach (DataRow personRow in person.Rows)
{
Console.WriteLine("{0} - {1}",personRow["Id"], personRow["Name"]);
foreach (DataRow petRow in personRow.GetChildRows("PersonPet"))
{
Console.WriteLine("{0} - {1}", petRow["Id"], petRow["Name"]);
}
}