I am fairly sure the one critter that is fairly obvious is some type of insect larvae or an insect. I'd get rid of it, it may be a carnivore. Most surely not a baby fish of any kind. Some insect larvae can be harmful, I make a practice of removing any I find, unless the fish are eating them.
The picture I see is no insect larvae. Sadly, I've spent a lot of time looking at them.
Amphipods, aka scuds, don't look like that. I've cultured them as fish food and I'm sort of fond of the little guys. They are slender, and seen from below, have a lot of legs, looking very like shrimp to which they are related. They usually stick close to the substrate, move fast, can look like they are 'hopping' from place to place.
There are hundreds, if not thousands, of species of copepods, amphipods, and the like. In FW, SW, and in between.
They hide mostly, being prey items, often come in on plants and are essentially harmless, unless you have newborn shrimp. They have been known to predate oin the odd newborn shrimp, but are not likely to kill many of them unless you have hundreds of scuds and they are really starving.
I think the pods dining on juvie shrimp is urban legend, internet style.
Scuds will eat plants if they are hungry.. so having them in a planted tank is perhaps not such a great idea. They prefer algae, but plants will do if algae is not available.