I want a dog, but my mom refuse to have it now...  

It sounds like a dog right now isn't the best of times. A lot of things are going on at your home and maybe it isn't the right time to have a puppy. Your Mom has a lot of responsibilities, and she may not have the time (or especially the energy) to deal with a new puppy. Because of the new baby, most of her time and energy is into taking care of the baby. She also still have 2 other children to raise. The only way you MIGHT be able to show her that you can handle a dog is to take up more responsibility in the house. Maybe do some chores without being asked. It's not going to happen overnight and it may not happen for a few more months, but showing her that you are responsible may have her think about it a little more. And if you do get the dog and she does have guidelines (like you have to walk it, feed it, clean up after it), I definitely suggest that you don't argue otherwise you may lose the privilege.

Well i think you have to let her know that the dog will be your own business to raise it up& look after it& also take care of it..but there is nothing wrong if the dog hangs around the baby we do have cats&Dogs around our neighbours baby& nothing happens!