You'd be surprised (or not) how often I get asked about the order that the Hero Kids adventures should be played in. I've never stipulated an order for the adventures, and they're designed to be as stand-alone as possible so that you can pick and choose which one to play based on your time and player's capabilities. Having said that, this rough order might give you some ideas:
• Basement O Rats (Easy)
• Curse of the Shadow Walkers (Normal)
• Escape From the Ghost Pirates (Normal)
• Wizard's Tower (Normal)
• Fire In Rivenshore (Normal)
• Yuletide Journey (Normal)
• Mines of Martek (Hard)
• Tomb of the Lost King (Hard)
• The Lost Village (Hard)
• Glade of the Unicorn (Hard)
• Maze of the Minotaur (Hard)
Mines of Martek and Tomb of the Lost King could probably go earlier if you tweak their difficulty a little bit.
Hero Kids dad Michael Henry has other ways of connecting the adventures into a campaign:
"Zimarim the Grim is an evil wizard that has attacked and all but destroyed the town of Willowsdell. He did so by several long-forgotten magical attacks. During these attacks, a hero by the name of Barnabus Longwillow left Willowsdell in search of the one laying siege to the town and a way to undo the magical destruction happening all around him. He happens upon a pool of water in a cave beneath a mountain on the far side of the bay. Thinking that this was the source of the magical attacks on his town, he took out his Great Bow and fired upon the water spirit within. The spirit turned him into a giant rat and laid a spell on him that trapped him in the caves where he found the pool."
Hero Kids Campaign - Campaign Overview