The Petzl Aspir climbing harness for kids size 0 is an excellent choice for kids.  It is a multipurpose adjustable climbing harness that is lightweight and comfortable.  Padded leg loops and waist belt make this more comfortable than most rentals. 

• Petzl Aspir Climbing Harness for Kids
• Comfortable: foam waist belt and leg loops
• Single Dyneema attachment point above the waist belt for excellent abrasion resistance
• Easy to use:  webbing is grey on the inside and black on the outside
• The right leg is tagged to help make the harness easy to put on
• Quick adjustment with DoubleBack buckles on waist belts and leg loops
• Two flexible leg loops on waist belt
• Youth size: 0
• Certification: CE/UIAA
• Sizing: Waist 23.5 in , leg loop 16.5 in
• Weight: 404 grams / 14 oz