depends on the colour and if its a natural dye. (which i suspect that fruit loops dont have , apart from uk ones that do, but thats another story)
anyway natural pink or red dye is made from crushed beetles, and so contain a protein, and can be a problem for some.
that said, if on a particularly sensitive day for your child, eating something with such a long list of ingredients that are chemical in nature iyswim, might be a problem. My son after a reaction would react to other stuff like this for a while until it was removed and settled down after a period of time.
So my personal rule of thumb, if you dont understand the strange names on packet, and its list is more than a inch long, try to avoid. The longer the list, the more difficulty tracing cross contamination, think of the transportation to the food manufacter of each different thing on the label, think of the staff, think of many, many different lines that are shared , alongside each other etc etc etc.
food is vastly complicated these days.