My 3-year-old is around 37" tall and a chunky 32-ish lbs ... and she's still got quite a bit of room to grow in our Toddler sized KP.
I would HIGHLY recommend trying to find someone who has a Standard and a Toddler to try it out and see if the Toddler one would be too big.
What are you currently using? We were using an Ergo & my daughter leans. The KP gives us a taller body & wider seat, so she's less likely to lean.
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Liz
DD (3/2010)
"Make mistakes! Get messy!" - Miss Frizzle