Sizes? They appear small! Agree with fancy that we need a pic of the back as well. They do appear to be the type of pics that were sold in stores like JC Penney, Sears, etc.
Utrillo painted many scenes using Montmartre as the background with the windmills and street scenes.
Does it appear that the pictures were painted with "white paint" on the background before the scenes were painted or that the background was painted with a white paint? (Utrillo's works were highly regarded as "white mannerism" paintings) If so, take them into the dark...when you look at this type of painting in the dark the whole painting will appear white (an odd glow to it). The white areas will appear dark. The colors that aren't white will appear white in the dark. (Much like a photo negative is opposite of the finished picture.) The colors will "behave" like they are white, thus "le mannerism blanc". It is believed that Utrillo achieved this effect by mixing lime (the kind used for landscaping and sports fields) with the non-white paints.