Birth records did not start until 1914, so your not going to find Bertha Young 1901-02 Or Lennie Young 1907-08 other than on the 1910 census using Lawson, have you checked with church records, baptism, school records would only show Lawson name. And not knowing the first name of her 1st husband one can only assume he died right after Lennie was born, since she remarried in 1909. Was not able to find a marriage for a Ella Belle or Ella or Belle to a "Young" that made since. Have you found Belle's parents?
You might want to use familysearch.org to see if they have info ancestry does not.