I think these shots are of very good standard, and yes, you should charge for sessions.
It is not about how much you charge, it is the fact that people understand that you value your skill and time enough that you will not do it for free. If you are uncomfortable with whether or not / how much you should charge, why not do the session for free, but then your clients only pay for what they want? You can make the amount a summountable sum ($150 per image for example) or rather piddly ($5 for example). As long as you are honest and up-front about the costs, your clients will be too - and the fact that they only pay for what they want is a fair, and open ended way of doing things. You will also quickly learn that when people are paying for images, they suddenly become a lot more critical...so get your thickest skin on!
And as a by-note, Walgreens (I guess the same As ASDA and BOOTS here in the UK?) will offer a crazy variant in print quality. I have worked with minilabs for nearly a decade now, and it is remarkable how much tlc the chemistry and racks need to consistently produce high quality prints. That is the key - consistency. You are much better off going through a pro-lab, whose sole job is to produce your images to their consistantly excellent standard, than you are a shop which sells jeans and pineapples on the side. You may get excellent prints 10,20,30 times from Walgreens - but if you go in and get them done the day the chemistry dies, you will be utterly disappointed. Trust me.