Our kitten died & my 7 year old is heat broken.....?

our cat Itsy had kittens and one was very very small.she looked liked a chiwawa so we called her Chi-Chi.because of her size i made sure that she always had a tit to feed on and if not i feed her myself and help her use the bathroom.i kept Itsy and her kittens next to my bed so i could keep an eye on her through the night.Chi-Chi was the first to open her eyes,the first to walk around,the first to eat on her own and the first to use the litter.when she hear my voice she'd come runnin to me.but sadly,on April 15 at the age of 4 weeks and 5 days old,she ped.i cried very hard for her and still do but my 7 year old son said to me,"i don't like God cause he took Chi-Chi".i tried to tell him that God wanted to take Chi-Chi when she was born cause she was so small and weak but i wouldn't let him but when God saw her getting weak again he took her home.we barried her in the back yard and i made a special box for her with her name on it and told my son that's she's still gonna be home with us in our hearts,he still said,"God is mean,Chi-Chi is only a baby,why a baby?"is there anything else that i can tell my son that will help with the loss,he's 7 and we have 10 other cats but because of the care and love we put into Chi-Chi,he loves hr the most.i still miss her.