If it's that frizzy, you may want to consider getting it chemically straightened - most afro Caribbean salons offer that service and usually have childrens products available.
Despite having 2 white British parents and 4 white British grandparents, I've got afro Caribbean hair which I get chemically straightened every 3 months. Growing up in a very small rural village, I got bullied horrendously for my 'frizzy' hair and picked on by both children and adults (called a 'freak' in the local post office) - Think of what Michael Jacksons afro looked like... then think of a female child, with BLONDE hair....
I started getting it braided at 16/17 and whilst the school refused to begin with, my Mother threatened to go to the papers for racial discrimination as black girls were allowed to braid their hair, yet the school said I wasn't. The school relented and I kept my hair in braids until I was 22, when I switched to chemical products and have never, ever looked back.
If my hair was 'natural' it would be so wild and frizzy, I don't think anything could make it look 'calm'... I also know if I kept straightening it with heat - it would break off and become very brittle and even worse.
Sticking the normal types of hair products you find in Boots on hair that's really frizzy doesn't always work and can just make hair 'claggy'. I tend to stay faaaar away from things like 'frizz-ease' which are expensive and useless (in my opinion) and buy specialist ones from either the internet or afro Caribbean hair shops which are cheap in comparison.
The Fantasia IC range is amazing - 'Fantasia Ic Olive Moisturizing Shine Serum Hair Polisher' and the one with the white top are my lifeline - they keep your hair moisturised and shiny but not greasy or claggy and you only need a very small amount, even on thick, frizzy hair 