Moving from free to paid work

Hello, I'm having some trouble managing levelling up my photography from free to paid. I have several friends I have shot for free and I am now wanting to move to charging to build my business as I am getting more inquiries organically which is what I wanted. I feel very awkward about offending people who I previously worked with for free by now stating that I'd be charging them. I also volunteered to shoot a couple of events last year and now they are asking me to come back and they are for charities so I am feeling badly about charging them but I also don't want to work for free forever. Any advice from someone who has gone through this?