A better understanding and company play more important roles in children's growth. 

【翻译】更好的理解和陪伴在孩子的成长中扮演着更重要的角色（起更加重要的作用）。

understanding 是名词。是一个可变名词（可数不可数均可），当前面有修饰语（better）时，多用于可数名词，强调是“形象化、具体化的理解”。看英文注释：

可数：N-COUNT  If you have an understanding of something, you know how it works or know what it means. 

不可数：N-UNCOUNT  If you show understanding, you show that you realize how someone feels or why they did something, and are not hostile toward them.