We went last year when my LO was only 16 months so still in a highchair but very distractible. We tried to go when it was quite and found tables outside where there wasn't so much going on. We are going again in September and will not let him leave the table (either me, my DH, or my parents will get his food for him) He understands he cannot leave the table without asking at home so hopefully that will apply on holiday. Hope it is not wishful thinking on my part.
Also in all inclusive there is usually food around almost all the time so we didn't worry too much if he didn't eat at one meal as we could still get food and not worry that he didn't get enough.