Conditioning spray - you can also use a de-frizzing serum after washing to reduce frizz and that helps tame it for a while longer (John Frieda is really good)
We've been trialling loads of products for my boys mass of curls. So far I find the best thing is spraying down with water and using a bit of cantu kids curling cream holds best x
For my little girl, I use a water spray before brushing (this also helps brushing) and then a curl custard from My Little Coco. Her hair generally stays curly and not frizzy all day.
I use the Johnson’s curl spray conditioner and my little coco curl custard x
Try some leave in conditioner. We bought some from soap for little suds. Xx
Maybe it needs more moisture? I’ve been trying different things with my daughter too and I think like just straight water or water and a little bit of conditioner. Or even like wetting it then a leave in conditioner can help. She still has super short hair so her hair just scrunches back up. But for longer I’m not fully sure.