Honeydew, if you didnt want to b/feed your children beyond 12 months that is of course entirely your choice.
That doesnt mean children don't "NEED" to b/feed beyond 12 months.
A child can probably get most of it's nutritional needs through diet from beyond 12 months, but b/milk is full of nutrients and antibodies and all comes in one, easy to digest, readily available source. Why wouldnt you take advantage of that?
12 months is a good start to the immunity, but b/feeding continues to boost this for as long as you do it, and as discussed below, a child's immunity isnt fully formed until they reach 6 or 7 years of age.
Why do you think 2+ years is too old? What makes it appropriate at 729 days old, and inappropriate at 731, 732, 733 etc days old?
There are lots of valid reasons for discontinuing b/feeding. But, tandem b/feeding is very possible, should you want to do it, and quite a few mothers on MN have done so. If you didnt want to continue, or couldnt, then that is fine by me, but, I'd hate to think you were discounting it for a reason that could be overcome with the right support and help