Function parse_child 

pub fn parse_child(
    ctx: &mut SpendContext,
    parent_coin: Coin,
    parent_puzzle_reveal: &Program,
    parent_solution: &Program,
) -> Result<Option<ParsedOption>>

Reconstruct the option child created by spending parent_coin, given that parent’s serialized puzzle reveal and solution (both fetched by the caller).

Returns Ok(None) when the parent spend did not produce an option child (its puzzle is not an option contract).