Your post if very vague about what the conditions are. I do believe that young children normally have a higher (than a young adult) HR.
Have you discussed with your (child's) doctor? It may be the irregular HR needs to be recorded for medical evaluation. Your doctor will know what and if anything is needed.
Otherwise, be calm and positive. Raising children is very stressful when we think there may be something wrong with their health... don't jump to conclusions.
What do you mean by irregular?
My daughters heart used to speed up upon inhaling and slow down as she exhaled and I used to think it felt irregular when in fact it was a normal sinus rythym. It is actually a sign of good health.
And yes, young children do have a faster heartrate then adults.
Jodie