If you look on page 8 of your Player's Handbook, you'll see a section titled "Rerolling." It tells you that your scores are considered "too low" (and may be rerolled) if your highest score is 13 or lower.
I'm bad at this but. .. .
I think the odds of getting one 6 are one in 6 (16.66%?). The odds of two 6's = multiplied by 66 (36?). One in 36 rolls comes double 6.
The average die lands on 3.5 and 3.5 x 3 = 10.5 average. Adding another die (4d6 remove lowest) adds a 16.66% chance that one is higher? raising the average to 11.5.
The odds of rolling 3 sixes is 215 to one. Oh wait, i think i could find a
link
On four dice the odds of a specific(6) 3 is 64 to one.
With your proposal the odds of getting either a 6/6, 6/5, 5/5, 5/6 are 1:8.5.
The odds of having a +2 ability bonus in a specific stat are 54%.
The odds of having no bonus in a specific stat are 8.5%
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I've been dealing with this since about '78. I think the point buy is best, but don't expect the rolling of stats to go away. I have a favorite method, which i offer my players. (I always roll epically hot for the first abilities of my character.)
You can take the point buy(32)
or
You can get a sheet of ruled notebook player and start rolling 4d6 drop the one. Write the numbers from top of the page to the bottom. Highlight any 6 you want.
10
14
15
8
12
15
11
10
17
7
11
16
13
14
12
10
16
5
14
It hold the bell curve fairly well, and i've never seen it give a set of numbers greater or lesser than i could put up with. And it let's the kids roll the dice, but it's fair. Works every time.
If they're not happy with such an offer just give them whatever stats they want. It will be lower than what you've offered. heh