The professionals on this site are going to tell you that you need to get one. I think that some things come into play here. Do you have E-gress windows? Or basement access? If you plan on including the sq. footage someday when/if you sell it then you might want to get a permit. I am in the process of finishing my basement right now and I did not get a permit, however, I am making sure that certain things are done to code. (i.e. GFI in bathrooms, proper plumbing, etc.) Since I cannot count this as liveable space when I do sell it, I can count it has improvements, and I still want it to be ok when an inspector goes down there to check it out. I have got 4 of my friends doing their basements and none of them pulled a permit but did everything to code. In fact, someone I know did pull a permit because he is very conscious of things like that and they turned around and added $100,000 to his tax bill. Again, I am not a professional, just a DIY, but this is the info that I have gathered myself.
I finishing my basement for my 1 yr old (and his toys), congratulations on your new baby!