I haven't yet been to Gumbet before but once stayed outside of Bodrum which is in that area of Turkey.
Temp wise it should be nice there then. I would imagine it would be mid 20's so very pleasant, might get a little chilly in the evenings though so do take some things to wrap up LO.
I am pregnant with my first so have never been in the baby mindset when i've been there before but i would advise taking the key essentials with you as im not sure they would have everything you need as the shops aren't anything like here with mountains of choice for everything, not often are there supermarkets but more lots of what we'd call small convience shops or like corner shops. They would have more in the bigger cities like in Bodrum for emergencies if you desperately need something but would be a bit of a trek!