Getting parents on board is one of the trickiest things, especially when there is EAL at play or if they are working.
It's really important to have a whole team strategy for working with parents and talking about their child's communication should be a big part of that.
Its best to have a two-pronged attack strategy here:
For settings where parents come in frequently or there are frequent meetings, consider using resources such as those produced by ICAN. These include communication posters, first words poster as well as handouts for parents/carers. You can also generate some of these yourself if if you feel that you have the correct information. Bear in mind that this does need to be talked about sensitively - no-one wants to think their child is falling behind and some parents will go into 'shut down' mode.
For parents who don't attend frequently, there is EAL to consider or absent parents it would be advantageous to arrange meetings with parents either on a 1:1 basis or group sessions to explain how communication works in your setting and what the expectations are. You can share information this way and keep touching base every so often at a time that suits them. You could also utilise your website or social media streams to ensure parents get the information they want at a time to suit them.
The following toolkit is available on the ICAN website and is a good place to start when working with parents on communication.