Are My Twins Developmentally Delayed?

Will and Jeff will turn three on March 23, and they are sheer delights; easygoing, happy, healthy, filled with wonder at their world. They just seem more than a little pokey as far as learning things like body parts, ABCs, colors, animal sounds, etc., as well as fine motor skills like holding a fork/spoon. They enjoy reading tremendously and freely choose to read to themselves after most meals, although for the past four or five months they seem to dislike sitting in my or my husband's lap to read, maybe some kind of control thing ,lately. They're very physically adept, into climbing and other gross motor skills, and Jeff ,in particular ,delights in hanging from the top of the swing set/jungle gym . He also enjoys playing basketball. Although I do restrict TV watching to one to two hours per day they're not terribly interested in TV or videos except for a few Winnie the Pooh tapes. They undress themselves and Will lately likes to try to reverse the process and re-dress himself after undressing, although other self-care steps like bathing and using utensils at dinner are of little to no interest despite our encouragement.

Both increasingly are verbal, especially Jeff who's into whole sentences and initiating a conversation with me. Will tends to sing more than speak and only ask for something by name if he really wants it, not to express a thought like Jeff will do. Yet Will is interested in toilet learning lately,(still a ways to go )but he has learned the after-the-fact feelings and will sometimes run to the bathroom when he thinks it's "time." While both know their names ,Jeff will more consistently tell you his name, although neither will state his age or even get real excited about the upcoming birthday. They still go through hard bouts of separation anxiety. We're in the throes of one again now, where even Dad won't be of any comfort if it's Mom they miss, even when Mom is just around the corner in the shower.

I'm not a flash card mom but I try very hard to expose them to all sorts of experiences. I work part-time three days per week out of my home and do lots of enriching little kid field trips etc., on my days off, and try to create an enriching yet safe and consistent environment for them. I see the other little boys in our neighborhood (there were seven boys born in a nine month span here) and note that most of them are "further along." I truly feel my kids are right where they're meant to be today, and that I'm doing the same things I did for my daughter (albeit that she was an only child back then) that allowed her to blossom. However I'd like to know when to be concerned, and when it's just an individual variation in development.