Just to be upfront, I am not hispanic or bilingual so I have no real firsthand experience other than what I saw growing up with lots of bilingual friends. I grew up in california in a very diverse school district, so my opinions are based on that.
I think it would be good to put your son in some kind of program, whether it is daycare or some kind of dual language program. At 2 1/2 i don't think there is any teasing or making fun of children yet. At least not in any of the playgroups we have participated in. My son is 2 1/2 and I have never seen any of the kids his age make fun of the other kids. Some of them aren't talking at all yet. I really think there is nothing to worry about there. In a year or two, it could definitely happen. So I think it would be better to do it now, instead of later. My nephew is also 2 1/2 and doesn't talk much. Recently he was here on an extended visit, and I babysat him weekdays every day. My son is an early talker, and he and my nephew and played great together. Sometimes my son would ask me something that I knew had to do with not understanding my nephew, but there was nothing mean-spirited about it all. And it was good for them to be around each other, I think.
As far as forgetting his spanish, as long as you speak spanish regularly at home with him, I don't think he will forget it. I had a lot of bilingual friends that spoke perfect english having been brought up from birth in the US, but whose families spoke the other language (spanish, vietnamese, chinese, cambodian, filipino) at home, and they were fluent in both. And when I would go to their houses, the families would speak some english (some of the family members were more fluent than others) which was nice in my opinion, since I didn't feel uncomfortable.
I don't think you have anything to lose by getting your children in some type of program early on. It will make a world of difference in their educations, social lives, and future success if they are comfortable speaking english before they start school. Being bilingual is going to give them a huge advantage. And there is no reason to think they will forget spanish if they are exposed to it consistently. Hopefully someone will have some good advice on what kind of program to put him in. Good luck!
Oh, PS, your english is great.