Les Mis - when Fantine is dying and she's hallucinating that she can see Cosette. When she says to ValJean, 'take my child, I give her to your keeping...' 

The end of Marley and Me, 'you were a great dog, Marley'
The end of Mamma Mia 2, Donna and Sophie singing in the chapel, '...you're my one and only...' - DD is my only child and this bit makes me literally howl.
It's A Sin, Colin dying, 'I don't want to die mammy' 
I, Daniel Blake - Katie's speech at the funeral
War Horse, (play and film) - too many to mention, but the bit where Topthorn collapses and dies is particularly 

About Time - when they have one last walk on the beach together
Inside Out - Bing Bong, 'take Riley to the moon for me' 
The Good Dinosaur - when they communicate that both of them have lost their families
Black Beauty - Ginger being cruelly abused and then dying