hair products

both of my kids have wavy to curly hair. I really want to know what are the best products for their hair, I have straight to light waves. my four year old curls look like they are dying down and I really want her hair to look nice and healthy and curly as it once did. what are the best products to curly frizzy hair. her fly always never stay down no matter what products I have tried so far. my 8 months hair has more defined curls starting to come out I don't want to mistreat their beautiful hair