Eldest is 2 & a half, youngest is 6 months. So I understand the 2yo is more ‘fun’ & easier to interact with.
If we go to see family, they all fuss over DC1 & don’t even look at DC2 (honestly not exaggerating) till 15 minutes later when they say ‘oh hiii x!’ Baby really smiley/happy/content. Breaks my heart when they give a big grin after being shown a bit of attention at last 
Another really silly thing... my mum made them both matching stockings & I noticed she gave the worse looking one with some imperfections to DC2.
I already feel bad myself on DC2 tbh, that DC1 gets more of my attention because they’re more demanding/older, so this may be clouding my judgement.
I feel a bit ridiculous now I’m writing this down really... but it feels real to me, I feel horrible.
Has anyone else experienced this with your youngest, especially if they are close in age?