According to Rashi, the Plague of Frogs during Passover "was only one frog, but when they struck at it, it was split into many swarms."
So if you want a biblically accurate Seder, I suggest you get a frog piñata and fill it with frog shaped candies.
@LilahTovMoon tldr for anyone not well versed on somewhat-obscure Torah shenanigans: it stems from a weird transcription issue(?) where 'frog' was written in the non-plural form in one spot, so while "plague of frogs" was the threat given to the pharaoh, apparently g-d heard "plague of frog" and answered with (presumably; size is never mentioned AFAIK) frogzilla.