I'd try and anticipate the biting behaviour and then distract Jasper with a toy. Rory (7 months) will mouth if he gets over exciting during play or when I return to him so I always aim to keep playtime calm (but fun for him) and channel his biting onto a toy. If he does bite me then I too make a "ow" sound get up walk away and end the game. I then return when he is calm.
As others have said I wouldn't scruff any dog as this could potentially escalate the problem from play biting to fear aggression - you don't want him to become fearful of you hands.
I agree - Coral is now 7 months old and doesn't bite at all....she does insist on washing my feet though
Using any form of aversive training is not recommended unless you are a dog behaviourist and even then it's all about timing and if you (or the behaviourist) get it wrong you end up with a ruined dog - this includes such techniques as water sprays......
I would consider when Jasper does the biting thing - is it when he's tired? Over excited? Just after he's been sleeping etc. if it's mainly aimed at your children, have they ever teased him as a pup? I'm sure it would have been in innocence but puppy play is never really just that, it's training a dog for the future - if they ran around with him following then that's all he's doing now, he thinks he's playing still
Get to know his trigger points if you can, then either avoid them which may mean asking your children to be calm around him, or find a good distraction as Emma has suggested. Failing that I would suggest contacting a behaviourist (positive reward only) to evaluate Japsers behaviour and gain some coping strategies.
I'm sure others will be along with more advice,
Jayne