I know that explicit images of minors are illegal, as it constitutes child pornography. However, is it illegal for a child to consentingly receive explicit photos from an adult?
First, the distribution of pornographic video is technically illegal in Australia except in the ACT or NT. This is because such films either have an X18+ or RC (refused classification) under Australian censorship laws and all state make these classifications illegal to distribute (not to watch or possess). So sending a video to anyone is illegal albeit it is an offence that is rarely prosecuted.
With respect to distribution of explicit material to children, this is the crime of “Procuring or grooming child under 16 for unlawful sexual activity”. In NSW this is detailed in s66EB of the Crimes Act. The maximum penalty is 14 or 10 years depending on the age of the child. Note that a child for this purpose is anyone under the age of 17.