HP - you say 'on them' - ie spilt on foliage? Well, yes - scorch - same like water. And many feeds are suitable as foliar feeds.
Although 'seedlings' would not benefit from a feed, it would not have got to the roots - so no result from the nutrient make-up.
As to what for what, we use a 2-1-4 ('Tom') feed on our cus. As recommended.