The first step is to assemble the KALLAX unit, according to IKEA instructions.
Then lay it down and on the short side of the KALLAX, screw in four CAPITA angle brackets. These CAPITA brackets are designed for holding up kitchen shelves/ worktops rather than serve as furniture feet, but they worked out perfectly.
Alternatively, you can leave your KALLAX unit on the floor. Lifting it up on feet gives it a wardrobe feel and a more ‘finished’ appearance. The legs also add more height for fixing the clothes rail to either side.
The unit is quite heavy, so use heavy duty legs with a decent fixing plate to spread the weight.
Total cost for this DIY kids custom closet is $250 (not including repairs/flooring after demolition). If you want to push the cost even lower, you can go with basic cube boxes, instead of drawers and cupboards, and forget the feet.