Cardiologist read qtc if 453 in a toddler. is this something to worry about? getting it checked again in a few months

That's normal: A qtc of 453 ms is normal, albeit, at the upper limits. Causes can include low potassium, calcium or magnesium (baby having any recent diarrhea or vomiting?). Many drugs can cause this too. Is there a family history of sudden, unexpected, premature death? If not, i wouldn't think much of this - long qt syndromes tend to run in families.

Long qt: Assuming no concerning clinical history, i would say just follow up and don't worry about it for now.

Probably not: Any family history of long qt syndrome? Was it actually personally read by the cardiologist or only computer-generated reading? Computer readings are often inaccurate. Follow-up can't hurt, but, at best, .453 is only borderline. Probably normal.