Cressi Rocks Kid Fins Adjustable Premium Children Snorkeling Fins Unisex

My daughter is 10 and wears a girls 4-5. Will the small be ok?

What size Is small medium versus medium large?

What is the total lengh of the fin? I wonder if they would fit nicely in a suitcase for travel. Thank you.

My son wears a youth size 4-4.5 in sneakers. Would he be a s/m or l/xl in these flippers?