Why can't I send/receive text messages using wi-fi only????

[AC Question]

I hope someone can help. I no longer use my Samsung Galaxy S3 (prev with Sprint). Want to let my children use it to send/receive text messages to their friends. For some reason, this function does not work over wi-fi yet I can still browse over the Internet. Have searched all the forums and can't seem to find a question/answer related to this specific issue. I hope someone out there can help. I know it's an S3 phone with a lower priority status, but would really appreciate if someone can tell me if this is even possible and if so what type of settings/apps I need on my phone to make it work. Please, pretty please anyone???? Thank you for reading this.