From the plot's perspective, Sangwoo's most important relationship was with his mum, now Bum is her "replacement" to an extent. Therefore the scene with the child whilst out shopping was likely to try and convey that Sangwoo was reflecting about his own parent & child relationship, which is something that he struggles with and is conflicted about.
Its showed a bit of Sangwoo's inner thought but i would go as much yo said he's reflecting *cough* im so sorry, that was just somehow runs a chill on my spine.. Reflecting..
*i wouldnt go
Why does it feel like sangwoo is bringing them both to their death? Also Sangwoo doesnt care about his facade anymore since he had bum on his side this latest chapter. we even get to see him jealous over the mention of bum's uncle so as his care for kids.
This chapter feels like 'last supper'. In which they enjoy everything else before their death.