Well I'd say, as a gamble of course, the uncirculated sets have the most coins and the cheaper price, the the greater potential for a true gem coin to be there worth some more money other than a bit over face value.
With the P's and D's there's a chance that any year the strike of one of the denominations, isn't that good and finding a MS68, MS69 or MS70 is really hard to come by but could be gotten from the set due to more care taken at the mint. Not saying it happens just saying the possibility exists.
We do it because we love coins in general, so I guess if your kids love coins and would cherish the sets more than ice cream or candy, maybe it's a good idea.
probably better to hold a "coin hunt saturday" or sunday and pick up a box of coins and show them what to look for and try and get them into the hobby strong first than just buying them sets of coins. You'd also have the memories of the hunts and the time spent together when they are off to college and then starting their own families to cherish.
If I got coins as a gift as a kid I was like "awesome!". if it was my bothers, they'd react like it was socks. LOL
it's not for everyone.
With Proof coins they seriously should be PR68 at worst, Likely PR69 or 70, because of the proof process, there will always be a lot of near perfect, or perfect coins. for this reason there isn't a huge upside to them, and why the coin shopping channels on TV love them, because they can get a bunch and sell it as "top graded" and the less knowledgeable might bite and think $50 for a $5 coin graded is a good deal since it's top grade.
Now I say "Gamble" because it really is, the likelihood you buy the sets each year and they don't go up in value and there isn't any condition rarity is real, but I think if you are going to do it, the uncirculated Mint sets would be the better route to go.
They would be right, that a retirement fund or a college fund a stock or heck, even a savings bond would probably be better than buying mint or proof sets in the long run.
Not only that but kids are kids and for the most part a coin is a coin to them, and when the ice cream truck passes by all bets are off on that set surviving. LOL
You have just as much chance of buying a newly released comicbook, baseball card, packaged toy ect, any "collectible", and seeing where it's at in 20 years, again a gamble. it's likely there isn't much if any appreciation of value, but, you might get lucky.