This might be Josh Kirby... Time Warrior!. It has time travel and an episode with giants.
The series concerns a device, found by humans in the 25th century, called the Nullifier. This device is said to be capable of destroying the universe. Realising the danger, a man called Irwin 1138 splits the Nullifier into six pieces, which are then dispersed through time. However, a scientist called Dr. Zoetrope finds out where the pieces are located and, with the help of his time traveling armor, sets about reassembling the device. Along with 20th-century teenager Josh Kirby, and a half-human warrior known as Azabeth Siege, Irwin 1138 sets about thwarting Dr. Zoetrope's plans.
Josh Kirby is 14 years of age in 9th grade and his journey starts when he is accidentally pulled into the fight between Irwin and Zoetrope when a piece of the Nullifier lands in his time. He has to overcome his homesickness for small-town America, helped by befriending the alien warrior-girl Azabeth, and saving her life, a result of this being that she is bound by oath to protect him. After a series of adventures including seeing the year 70,379 where humans have become tyrannical giants, a world populated by living toys, and Azabeth’s home world where humans are the hated enemy of her people, The Kang, he eventually is confronted by a shocking betrayal by Irwin before he discovers that he must choose between Azabeth's survival and fulfilling his Time Warrior destiny.
The episode with the giants might be "Josh Kirby…Time Warrior! Chapter 2: The Human Pets"
So Zoetrope manages to escape and Josh and the gang head off in search of him, eventually landing according to Irwin 1138′s calculations, in 70,000+ AD, where they are captured by giants, which it turns out is a child that believes they are toys. Irwin believes that these giants are either descendants of the human race, or aliens that have conquered Earth. To make matters worse, they have been separated from their ship, which is on the kids 100 foot table, and they are also imprisoned with some other people who have been displaced through time, as the child forces them to pick up weapons and fight each other. Again, the fight scenes are very amateur, and the gun fight between two of the characters is rather funny, as it is simply the two taking it in turns firing shots at each other (all missing of course, from a range of about 10 metres), and moving in and out of cover alternatively. Eventually, the little kid gets bored and puts them all back in a box and goes to take a nap.