really no sense to buy a starter set, just buy a lanyard at the parks and save the extra money for extra pins on Ebay
We have been collecting since the first year WDW starting back in '99, my kids are now 11 and 7 - we have amassed over 10,000 pins - so watch out
We trade all day long - in between rides, on way in park, out of park, in each store... etc... just something to do as you walk to and from each ride, etc... We put 10 pins on each lanyard at day 1, and they trade away. They went thru 120 pins in 3 days, no problem.
Here lies the flaw to your thought process - on day one, they will be excited and trade their 4 pins each in about 10 minutes. If they happy to "like" one of the pins as a "keeper" - now they only have 3 to trade again, etc .... you will probably be done for the day in an hour. Not how you envisioned a day of pin trading?
Instead of the structured way of giving 4 pins a day - fill their layard with 8 - 10. Let them trade away. At the end of the day, let them take off their keepers, and restock the lanyard. By day 3 - 4 - they will probably think all their pins are keepers - but they will have no pins left to trade - this allows them to make decisions on which pins they like, and which they can try and get "better" pins with - letting them make these choices makes them appreciate the pins they have traded for even more - and they understand the concept that when there are no more "traders" left on their lanyard, they are done
this is my 2 cents
if you need to buy extra pins, I'm sure I can find some in my extra pin bags
have fun
- david