Маша и сын её, Саша, ходили пешком за покупками, а сейчас сынок устал.
The idea here was just to express this idea:-
'Masha and her son, Sasha, were going shopping on foot, and/but now the young son had become tired.'
So I chose ходили as I thought it would imply that they do this (maybe) every week; an ongoing habit, a tiring, boring routine. Also to express the idea that they were in the middle of their shopping related journey when the other events occurred. I hadnt given any thought as to whether they had finished buying the shopping, or not. Sort of doesnt matter in this context.
Are those good reasons to choose ходили instead of шли?