If you want good quality knickers as a multi pack without paying the earth choose these from John Lewis girl's range. You'll need to be around size 8/small 10 to fit the top size which is 'age 16', but the gusset is good and wide and I put them through the mill by washing them at 60°.
I wish they did other sizes, but they don't. I've hit a gold mine and I just wanted to share.
I've seen people asking about good quality knickers with good crotch coverage.
Here's the link: www.johnlewis.com/john-lewis-kids-plain-bikini-briefs-pack-of-5-black-multi/p3599536
N.B.They don't go over the tummy like a woman's 'full brief'.
I thought about buying from next but I don't like the cut or gusset when I took them out the packet in store.
I hope I help someone out.