In our work, we have adopted a coupled fluctuating dipoles method based on a microscopic approach that accounts for many-body interactions to compute the van der Waals forces in free liquid films. We have analyzed the peculiarities of the surface forces in films with thicknesses of a few molecular diameters, where the macroscopic theory is not applicable. The problem addressed in our study is related to the influence of the nanobubble size on the energy of the liquid film formed when two nanobubbles approach each other. It is shown that the decrease in lateral size of the liquid film results in the diminution of the van der Waals specific attraction, a change in the contribution of many-body interactions to the total energy, and variation of the thickness dependence of the free excess energy of the liquid film.