Childrenswear size grading for manufacture

I am in midst of launching a small childrenswear collection for early 2019. I'm working with a factory in Portugal and have had my samples made across the three items I'm launching with - but I need help in working out sizing grades to supply to them for all the size ranges. I'm aware that childrenswear sizing is slightly less generic than adult sizing and need some guidance! I can supply my tech packs etc for help..

The garments are:
Leggings aged 1-2 / 2-3 / 3-4 / 4-5 / 5-6 / 6-7 / 7-8
Dungarees aged 12-18mths / 18-24 mths / 1-2 / 2-3 / 3-4
T-shirt aged 1-2 / 2-3 / 3-4 / 4-5 / 5-6 / 6-7 / 7-8