Start with one scarf: throw it up with one hand, let it float, catch it with the other. Scarves fall slowly, which is why they work where balls do not.
Add the second scarf only once one is reliable. Throw the first, and as it peaks, throw the second from the other hand.
Expect many drops. Picking them up is part of the practice, not an interruption to it.
Juggling forces the eyes to track two objects across the body's midline while both hands do different things at different times. Scarves slow the whole loop down enough that a beginner can actually complete it, which is what keeps them practising.