I bought the red one in size 14 for my 13.5-year-old daughter (46 kilograms, 1.63 meters tall) with the idea that swimsuits should be bought exactly in the size so that they don't sag in the pool.
It is very beautiful, dries quickly, does not fade, and has not faded at all with the pool chlorine, even though she has forgotten it 2-3 times in the swimming pool without rinsing it out!
Note that the cut at the hips is quite high compared to other ARENA swimsuits (we have 2 other models and they are much lower), so it may seem a bit revealing to someone if the child is quite developed! Also, depending on the body type, it may need a larger size because it seems a bit tight around the waist. However, overall it is comfortable, does not pull, and does not bother her at all. I also ordered a black one in size 14-15, I will update once I see how it fits!
Update: The size 14-15 is not recommended after all! While it is excellent in terms of waist and hips, unfortunately, it is very revealing on the sides and definitely not suitable for intense pool movements!