Actually, it's not a chignon, it's a variation on a French Twist, and you need rats and a band to do it. (I did it once for a theatrical production of Cinderella; we couldn't afford a wig.) The "twist" is horizontal on the head instead of vertical, and the hair in the back goes straight up and rolls forward.
Unless the hair is at least 2' long, the style will require a LOT of spray to hold.
The headband helps to hold the style in place; it needs to go all the way around the head, the hair starts out underneath and folds over it. The band is wider at the crown and narrow on the bottom. I found the style easiest to do using a long, thin barrette underneath the roll. You also need two rats, I'd think about 4" would do for a child, maybe 6". (Rats are made out of lost hair you clean out of a brush. Take an old sheer stocking and cut it to about twice the length you want, then make a knot about 1/3 down. Stuff it with hair to the desired length, then knot again. The long ends are folded in to help hold the hair down at the back of the rat.)
Put the headband on over the hair, like a circlet. The side hair should be pulled over the band to the middle and crossed so the ends hang on the opposite side; I held that hair down with a long thin barrette. Pin one rat across the back of the neck just above the band; this one is for pouf at the back of the head. Then roll the ends of the remaining hair around the second rat, pulling the hair straight up as you go. You want to pin the resulting roll right at the back of the crown of the head. You'll need to carefully arrange the "ends" of the roll so that the rat doesn't show, then spray the heck out of it. Using another piece of old stocking to smooth the back avoids squashing the 'do; spray the hair, then hold the ends of the stocking and slide the fabric gently along the hair between your hands.