These notched criss-cross style tenon joints give corners a little extra stability and increase the amount of surface area for glue-up.
When I build children’s furniture, I like to use the modified mortise-and-tenon joint you see here to connect legs and aprons. Instead of stopping both mortises short of touching, I run them deeper into the leg until they crisscross. Then, I make the apron tenons haunched to accommodate one another. That way, they interlock inside the leg, and the longer tips of the tenons extend into the deeper portion of the mortises. I think the extra-long tenons give these joints more glue surface area and strength than shorter tenons.
