Young children are highly regarded in Guatemala and can often break down barriers and open doors to local hospitality.
However, Guatemala is so culturally dense, with such an emphasis on history and archaeology, it's easy to overwhelm kids. That said, the ruins at Tikal should inspire all ages – if scrambling over ruins that aren't just home to an ancient civilization but also featured in several Star Wars movies isn't enough, there are also plenty of howler and spider monkeys to spot.
To keep kids entertained, try to make a point of breaking up the trip with visits to places such as Guatemala City's Museo de los Niños and Museo de Historia Natural, Autosafari Chapín, and Retalhuleu's Xocomil water park and Xetulul theme park. Most Spanish schools are open to kids too, and many older children will enjoy activities such as zip-lining, kayaking and horseback riding.
For general information on traveling with children, have a look at Lonely Planet’s Travel with Children.