Chestnut: Hero of Central Park (2004), Directed by Robert Vince – good movies with Makenzie Vega, Abigail Breslin, Christine Tucci, Louis Ferreira

Two young girls from an orphanage are adopted by a family in New York. The only problem is the apartment they move to doesn’t allow dogs. The girls try to sneak a puppy they find into the home and keep it hidden. Chestnut (a Great Dane) grows and grows while getting into more and more trouble.

http://www.imdb.com/title/tt0387925/