Since we haven't gotten any official word of the character's heights. This blog is here so that you can put your guesses. Here are my predictions
Ben - Ben isn't shown to be as tall as his mom or most other adult women in AF and UA so Maybe he's 5'3 minimum
Gwen - Gwen is shown to be a little taller than Ben, but she's not as tall as her mom either. Maybe she's 5'4/5'5
Kevin - Kevin is already shown to be as tall as most adult men, but he's not the tallest. My guess would be 5'9/6'0
Max - Kevin is shown to be taller than Max so maybe he's 5'10-11
Julie - She's shown to be shorter than Ben and Gwen so maybe 5'1?
These are just personal predictions. Since the character's heights change at various times, it's hard to tell how tall they really are.