Hey N.! I can relate to having a 2 1/2 year old that makes bad choices now and then, since I am a mom to one.
Do you and the day care center use "I feel" statements with your son? These are very big in the elementary schools and I feel they can be just as effective with toddlers. Here is what I do if my 2 1/2 year old hits. First, while I feel redirection is effective in most cases, when hitting or physically hurting another person (like his older sister) come into play, my son receives an automatic time-out. Children are very perceptive and to me a redirection in this case is seen by the child as a "freebie" (meaning I get to hit again before I get punished). For time-outs, I use the "minutes in time-out = age of toddler" and because he is two years old, he gets, at the most, two minutes whereas my four-year-old gets four (at the most--depending on the bad choice she made), and I don't plan to go past five minutes--even if they are six years old.
After the time-out, I talk a bit with my son using "I feel" statements, such as, "How do you think you made your sister feel when you hit her?" or "How does it feel if someone hits you?" We are a Christian family, so God often comes into the picture as well ("How does God feel when he sees you hitting?"). It may seem that your son is too young for this, and maybe he is, but my philosophy (in many cases) is "How will they ever learn, if we don't teach them?" If he is old enough to hit, then he is old enough to understand that hitting is wrong as well as the emotions tied with hitting.
Finally, my son always has to apologize to the person he hit (even if it's one of his parents!) by saying, "Sorry (genuinely) for hitting," and giving that person a hug.
While I can't say that my son never hits, he definitely knows the consequences (and emotions) that go along with hitting, and I feel this causes him to hit less.
Hopefully this was helpful! My apologies for it being so lengthy (I'm just a detail-oriented person by nature).
Sincerely,
D.
(wife and mom to 3 children)