It HAS to be on an odd-numbered generation. You know...1, 3, 5, 7, etc. First, get a toddler. It doesn't matter if it's a Marutchi or a Kinakomotchi. If it's a Marutchi, it will probably become a Hinotamatchi. If it's a Kinakomotchi, it will most likely be an Ichigotchi. Now, you HAVE to get either Ichigotchi or Hinotamatchi for this to work. Once you notice one or two hearts missing from EACH happy/hungry meter, leave it there for fifteen minutes, then fill them up. Keep doing this and generally just be a little bit forgetful of your Tama.
Did I help?