Children have higher heart rates than adults. If I remember correctly the limit for normal heart rate in children 2-3 years old is 120-140.
Heart rate increases with fever and is (again, if I rembember correctly) elevated by 10-15 BPM for each degree (celsius) the temperature is increased.
I can't say if this is dangerous or not because I'm not a physician. But I think (sorry to say) diseases and rapid heart rate in children warrants a visit to the physician instead of asking on a forum.
Sorry if the reply was a bit rough, but I think children's health is important. I wish you both the best :)
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