Not used them myself but just checked the local dive forum (where they were mentioned a lot, diver like bargains, it's a reaction to the cost of "genuine" scuba kit
)
Masks are generally thought of as good and a bairgain, just in case they've changed, you're looking for tempered glass and a flexible silicone skirt/strap for comfort and sealing. Really you should try them on and find one that fits but I imagine the lad would get by snorkelling if it's close and chap enough! (though do try if you can, if he folds the strap round the front of the mask out of the way and holds it (the mask) against his face in the normal wearing position, then gently breathing in through his nose should seal the mask against his face and allow him to remove the hand without the mask falling)
Fins seem variable, one et reported to have split after a giant stride entry, nothing heard otherwise.
If they're cheap enough then shouldn't be a worry for playing about with, and you can always pick up some cheap second hand sea fins(more scope for growing feet!) later if he likes it and they break.
A few BSAC clubs have snorkelling sections btw, if they get really into it...!
