I'm pretty sure the drinking age is 18 in Aruba. I get served, ive bought alcohol, everything.
Like ive said, ive been going to Aruba since I was around 10 years old, and the first year I brought my girlfriend with me, I was 15, and she was 17 at the time but looks much older. Well, we went to the Wave's Bar because we wanted to see if they would serve her and we would have a few drinks. Sure enough, they did, and they also served me. We found out throughout the trip that they served us at every bar we went to, including Moomba.
I'm not sure how old your daughters are, and how old they appear to be, but the one thing I love about Aruba is they are very laid back with the drinking age. I have honestly never seen them check someone for I.D.
Hope this helps.