From my perspective, it is better to wait until after having a child or two before inviting over other couples that have a child or two.
It would be very uncomfortable if its just the four of you, and half of you are pointedly not conversing with the other half. The setting is too personal.
Besides for that, until now contact with the opposite gender was always within gedarim, whether set by parents, yeshivah or shadchanim. It is not a good idea to put oneself in a situation where one might feel inclined to speak to someone of the opposite gender with no gedarim over you. By a newly married couple, the significant other may still feel uncomfortable telling off the other for crossing a boundary. It is best to wait a few years until the husband and wife can feel comfortable keeping the other in line.