
I always offer their porridge first then top up after, either from mum or bottle. Could be you gave them too much from the bottle, it is trial and error.
I do not use Burns, can only recommend what I use and that is either Pedigree Puppy Porridge or the equivalent from Eukanuba - have not had any problems with either. Did you mix the food with water or milk, that can make a difference.
It could also be co-incidence that you started their kibble meals, you need to keep an eye on them and if there is not any improvement it is a trip to the vets, as diarrhoea can be debiltating at that age if allowed to continue for long. Certainly if not improved later today I would pop into the vet.