Babies: Even babies a few weeks old are learning about sequence. If baby is hungry and sees you, he knows what happens next; you can see it in his body language.
12 to 15 months: Sequence experiments rule. She drops her cup, you pick it up. Again? Again? If you fail to fetch the cup, she drops a polite note in the suggestion box.
By 21 months: The power word "now" sees heavy use. "Soon" still means nothing to him. He can put together familiar clues and anticipate what comes next. "Mommy home?" he says when the Harley roars into the driveway.
2 to 2 1/2: Your 2-year-old lives in the present and uses words to show it: "Now," "dis day." He may be able to wait one nanosecond for his sandwich when you say "soon." The idea of "playtime after snack time" at day care means a bit more to him now. And he's starting to use words for the future, such as "I gonna." He has no words yet for things past, although he's using past tenses of verbs: "I goed there."
2 1/2 to 3: Her time vocabulary blossoms. Out roll 20 or more new time words, including some personal catchall terms like "last day" for the gigantic past. Sentences map things on a timeline: Me eat, then play.
3 to 3 1/2: Here, researchers begin to see wide variations in children's orientation in time. Mostly, he shows a more refined use of time words for sequence ("I had it first"), frequency ("two times today"), rhythm ("every Friday"), and duration ("it's a long time"). "Yesterday" debuts, but without accuracy: "I'm gonna see the ducks yesterday."
4 to 5: A child is at home, verbally, in past, present, or future and is getting verb tenses right. The words "day," "week," and "time" are dragged off the shelf a lot, with phrases: "every day," "summertime," "next week." She says and actually means "in a minute," "five minutes ago." She has some sense of holidays and birthdays. Most likely she can't tell you correctly yet what time she goes to bed or eats supper.
5 to 6: She uses most time words correctly now, no longer confusing the past with the future. She knows the days of the week and can tell you what day it is, what day comes next, how old she is, and when she goes to bed. She's using those expressions of the clock ("The big hand is at the bottom") but likely can't tell time yet.
6: He likes to hear about times past, particularly his own and his parents' misadventures. He likes to think about things in sequence. He travels in his mind into the future, anticipating holidays and birthdays. He has a notion of the sequence of grandparent to parent to child. He still likely can't tell time by the clock.
Beyond: A child in the years from 7 to 10 gains real competence with both clock and calendar, and the math to use in reading them.