When at work, my wife and I can’t always have the sound up to hear the kids Relay messages and headphones aren’t always practical. A visual “voicemail” for incoming messages would be a big help so we don’t miss messages. Speech to text would show the content of message to parents phone and possibly an opt in for adding the same feature to 3rd party app for kids friends.
The reverse could also be done where text messages from parent app could be sent as text-to-speech “voicemail” to messages channel. Again, an opt in for 3rd party account for kids friends could be an option so older kids/tweens could be in touch with approved friends without a smartphone/screen.
If this is not practicle, how about preset messages? ie. “I’m ready to be picked up”, “I’m home”, “I’m running a few minutes late”, “time to come home”, “love you”, “take the school bus home”, “staying after school” etc.