here in Fairfax County, VA - our local shelters have TONS of donated goods...
Depending upon the puppy, age, breed, etc. I would consider taking the puppy to a shelter or a foundation (Lost Dog Rescue Foundation, for example) to have the puppy given a home...
Children need to understand that pets cost money - yes, they are cute but they grow up...if you cannot afford it - then you need to give it up.. Yes, the children will be disappointed - but which would they rather have - a meal to eat or a puppy in hand?
Do not let the children control the household. I don't know how you took a puppy in anyway that you couldn't afford - you set yourself up for a fall on this one...sorry!! that's my take.
EDIT: I have to TOTALLY agree with Jen C - we purchase Eukanuba dog food and it's $30 a pop....we have to take Grady in for his 1 year check up and shots - that's $380......this doesn't include chew toys, bones, treats, etc...I spend an additional $50 a month on chew toys and treats...