What to do/say when someone is grieving?

We just found out a friend’s 2 month old baby has passed away unexpectedly.

I’m feeling so lost and heartbroken for them.

I’d really love some advice from people who have been through this level of grief on what (or if anything) we can do or say to be there for them.

I understand everyone’s different though.

We’re planning on sending some pre made food. I’m unsure of funeral arrangements etc but we could also make an offer to help there.

I’m also thinking of later down the track, once the initial shock and numbness has worn off.

For example: does it help to ask them about their child?

Does it help to message on the birthday/death day each year?