hi there ... sorry, I don't mean to say you should ring and ring and ring, several times a week or a day even - what I mean is, don't be disheartened if you call and have to leave a message, several times. IME this was because I was in pieces before the phone rang and couldn't possibly have spoken. but picking up a message and hearing someone say they were thinking about me, and thinking about DH was so comforting.
I don't want to make you feel under pressure to act, but just letting someone know you are thinking of them is fabulous. call again in a week, or two. it's about not letting things drop after a few weeks, but being there for as long as you can be.
Also, I do understand that you're grieving too and you will need your own time out and space to think about your friend and your loss. you also have your own life and dh and dcs who need you, and you need your own normal time when you get on with just being and put grief to one side for a short while. it is very early days for you all yet.
Just trying to give you a perspective from my own experience as someone who lost their partner very young and very suddenly - some of my most amazing support came from people who I had not thought of as very close friends before, or who were more DH's friends. and some of the most hurtful times were when I realised that to other of DH's friends I didn't seem to matter, he had been their friend so I wouldn't be seeing them again. Perhaps they were too scared to come near, or would say they didn't really know me, so no they hadn't got in touch ... but they knew HIM and that's what counted to me.
Losing people who knew your other half takes your beloved even further away from you, makes their life seem even more unreal. Friends sharing memories, usually happy ones, laughter and joy are what helps to keep someone's memory alive, for everyone who knew that person.
I hope this helps a little, please don't feel under pressure, I would only like to help you to help your friend and can simply offer the experience of having been through something very similar.