Guppies: Male or Female?

[Kaniela]

Aloha,
I'm new to these forums, and fish in general. Got some free guppies last month and bought a nice pair to breed.
One if my guppies just had about 26 fry on Tuesday.
They all look female to me. Do they all look female at the start and then develop into males?
How early can I tell them apart?
Thanks in advance.

 

[twiddlemuffin]

You won't be able to tell for sure for awhile I'm pretty sure.

 

[Kaniela]

Thanks.?