All you have to do to make them PCs is take them as written, re-roll their Intelligence (and in some case their Wisdom and Charisma), and add a character class. Voila! Instant(ish) animal PC.
Tiny beast, Lawful neutral
Armor Class 11
Hit Points 5 (1d6-1)
Speed 20 ft., swim 20 ft.
STR 1 (-1) DEX 13 (+1) CON 8 (-1) INT 12 (+1) WIS 8 (-1) CHA 3 (-4)
Skills Perception +1, Stealth +3, Arcana +3, History +3
Senses darkvision 30 ft., passive Perception 11
Languages Common, Amphibian
Amphibious The frog can breathe air or water
Standing Leap As part of its movement and without a running start, the frog can jump up to 10 feet, and high jump up to 5 feet.
Spellcasting This frog is a 1st level spellcaster, and its spellcasting ability is Intelligence (spell save DC 13, +3 to hit with spell attacks). The frog wizard knows three cantrips from the wizard spell list, and can have 2 1st-level spells prepared.
You can do all the work yourself in just a few minutes, but I'll keep posting other 5e animal PC templates, because I like the work for its own sake, and I figure someone might find them useful.