One of the best places to spend the day with kids in Guatemala City is Irtra Petapa. This park was created by the Recreational Institute of the Workers (IRTRA), and even if it sounds like a social country institution is funded and administered by private companies in the country, and one of the best examples on how private programs work in the country.
It includes a zoo, a dinosaur park, rides for children and teenagers, a pool, stores and a couple of restaurants. It is open, depending of the time of the year from Thursdays trough Sundays. Entrance is free for for workers in the private industry, and paid for government workers and tourists.