Summer is 4, 105cm tall and wears size 4-5Y
Caius is 5, 110cm tall and wears size 4-5Y

Garment measurements by size (approximately):
Size (cm) 18-24 2-3Y 4-5Y 6-7Y 8-9Y
Length 37.5 42 47 51 54.5
Front Chest 38 39 43 45 46