Ok, not too sure about the nature's diet junior (I'm not a nature's diet user but would think as with any dog foods, puppy is the one to use, it is specially prepared for pups, with vits, minerals, proteins etc for a pup and for their tums to handle, this may be causing the latter part of the poo's being more runny) I always give complete and fresh chicken or mince.
I'm personally not overly concerned as the poops are starting off solid and then the last bit being squirty, if that changes and the pups loose the solid and just squirt (Oh boy doesn't it sound awful

) then you need to get to the vets a.s.a.p a puppy with prolonged squirty diarreha (from 48 hours) will become dehydrated and can die, and therefore would need to be put on a drip for fluids.
The
best thing to give the pups now would be chicken and rice, it will bind the stomach and stop diarreha, that is if it is food related.
Stop them eating leaves, not good for them at all! Sweep up your garden and get rid of them.
If the diarreha sould contine after chicken and rice, then it can be anything from a tummy bug, which pups can easily pick up, to the more serious, if you have been worming with Drontal/Panacur then most of the worm type nasties will be taken care of.
If it should continue, collect a sample of their poops to your vets for him to determine what is causing it. And also try to watch and find out if it is all of them or one or two.
I hope it will clear up by tomorrow, and be nothing serious. :-)