Sounds like you depended on this place to supply your childs present and cake for his birthday.

Since my son was 1yrs old I have always planned his birthday parties way in advance...no matter where these were celebrated. And we celebrated at restaurants many times. But I always called ahead to make sure they had a cake and things ready.

Why wait until you get home to let them know you paid your bill but things were not up to your expectations?
You should always complain AT THE TIME OF SERVICE! Asking to speak to a manager is your right as a paying customer.