How do you say I love you baby in Spanish?
nena would actually be baby as in the term of endearment.It is the feminine form nene, and it used mostly with women.
If you're talking to a boyfriend/girlfriend or even a spouse, you should say, "Te quiero, cariño"
For more terms of endearment and romantic phrases, read below...
1) Cariño - honey/dear
2) Mi amor - my love
3) Mi cielo - my heaven
4) Mi corazón - my heart
5) Papi - Shakira says this..."daddy" (you could also say "papacito")
6) Mi querido - my dear
7) Mi angél - my angel
8) Guapo or guapito - handsome
9) Lindo - cute/cutie
10) Mi vida - my life
11) Mi rey - my king
12) Sexy - take a guess what this means in English
13) Bello - beautiful
More romantic Spanish phrases and words can be found here. (some of them are quite...steamy )
There a tons of ways to express endearment in spanish:
Te amo mucho mi amor = I love you very much 'my love'
Try looking some up as well, theres lots of resources full of them