How does Boohoo size up?

[2anddone]

Hello
I have never ordered from boohoo before but I have seen some Disney T-shirt's that dd would love!
She is only 10 but wears some size 4-6 clothes from Primark.
Boohoo do a 6-8 in the T-shirt's do their sizes come up large please?? If so I think I could give them as nightshirts!!

My DD18 is between a 6&8. I think they are pretty true to size. She's a 6 bottm and 8 top in Boohoo, Misguided and Pretty Little Thing