Hi all, 
I’m going to start off by stating this is my first time growing anything, I have zero experience so I’m open to all suggestions and opinions.

I planted some bonsai seeds around February 24 after germinating some seeds. Everything was fine until recently when 3 of my 5 plants have turned brown. I have no experience with bonsai and I’m eager to learn more about them. 
I will add some pics, but for context, we live in Ireland so they are kept indoors permanently. Have been feeding them a bonsai nutrients that I got in local hardware store from April till last week as the instructions said only give the nutrients from April to October. 
I got specific bonsai potting soil too. 
Any help appreciated 

These are not bonsais, but young tree seedlings.
These are not red, but green.
These are not acers, but spruces (picea)
These should not germinate in mid winter.
These cannot be grown indoors, they will die If not exposed to the elements. Which you have already seen by yourself.