The first time our youngest did one-to-one counting... I think he was about 18 months or so. DW and I just happened to notice that he was sitting there counting buttons on the couch. You could have knocked me over with a feather. Fast forward to today (about 30 months old) and he can easily count to 20... probably higher. But he doesn't always look at four items and say "four". Even when he counts items he sometimes just counts for the sake of counting and doesn't always make the 1:1 association. So he has the sequence and pattern of numbers and letters. And he knows that numbers are used for counting and letters for reading and generally, but not always, has the right idea on 1:1 correspondence.

The older child (now 5.5yo) I don't remember exactly. I do recall that he could easily count to 100 by himself very early on and got the 1:1 correspondence pretty quickly. At the time I was pretty clueless that this was atypical.

Both boys, however, go through intense spirts of intellectual growth. Then they'll level of for a while. Usually just long enough for me to think "eh. just a precocious child." Then they'll hit another spirt. It's too early for me to say about DS2.5. He's clearly smart, but don't know if he's gifted. For the older boy, we're pretty convinced at this point.

Never did any flashcards. For the oldest, just before he was 5 he taught himself how to count by Roman Numerals from leafing through a chapter book. A yowie moment. So about that time I started getting some educational toys like number blocks, fraction blocks, shapes, etc. Between that and talking about numbers and such at the dinner table we just talked about topics that interested him. Patterns have been a huge hit.

So personally--this is just me--I wouldn't get flashcards. But I would get number cubes and perhaps other math-related toys. DS5.5 has a number line in his room and a multication chart. Just stuff *he* likes and enjoys. We try to create an environment where they boys have toys they can help them learn. And then just talk about things, answer questions, etc.

YMMV...

JB