It mostly means "I always played outside after dinner", but with less certainty.
Modal verbs, such as "would" establish no time frame. The time frame is determined by the context. Thus you can say
"Yesterday, I would play..."
"Today, I would play..."
"Tomorrow, I would play..."
In your sentence, the past time frame is established by the phrase "when I was a kid", not by the modal verb "would".
Here's a future example:
"Next year I will go to the university. I would certainly study French there, but it depends on having enough time."