Often, when children reach a physical milestone, such as crawling or walking, they're so focused and excited about the new world that's opening up to them that other things, even toys, become less important for the moment. Once that skill is more developed, though, interest in toys and other things begins to resurface.
As for toys to entertain him at this stage, try picture books and toys that have lots of buttons and levers to press, twist and turn. Seven-month-old babies are also very interested in toys with surprises, as well as those that have put-and-take or stack-and-nesting features. Since your son is starting to walk, you might want to try an activity table or a push-behind walker so he could stand and play or use it for balance while taking those first steps.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.