As my daughters hair got longer it eventually got thicker and curlier. Probably about 6 months old I started seeing little curls coming through. I saw the most hair growth between 1 and 2. Now she's 3 and has has thick curly afro!
This can mean a few things one you may need to change hair products or two no offense your child may not inherit the thick hair gene then as others said your child hair may change as they age
Both mine were born with heads full of dark straight hair. It continued growing (still straight). At around 5 months curls started to appear. Both have different hair textures (due to being mixed) my sons hair is a lot more Afro and my daughter has very loose ringlets but both had straight hair until 5/6 months.
I have curly hair, and my sons started to curl at the back at around 11 months! He was quite bald before that, though 😁 his hair is still straight at the top at the moment, so I'm not sure what kind of hair he will have yet x