Adopting or having your own child ?

Ever since I can remember I have always wanted to adopt a child from Africa rather then have my own children. I have such a heart for the people living out there , and I am currently sponsoring two children in Malawi . I have talked to my mom about adoption rather then my own children and she doesn't seem to take it seriously , I think she would rather me have my own kids. Why would this be ? Is there something I should be concerned about when adopting ?