Hello. Thank you for your question. Most heart murmurs discovered on a child's exam are "Innocent Murmurs". These are normal and don't cause any problems. They can sometimes be a bit louder when a child is I'll and the body is working a little harder as a result. This is likely why you doctor detected it during an illness. I agree with him that it should be reevaluated after the illness to confirm that it is indeed and innocent murmur.
It is perfectly safe to travel and you should niy have any worry about this.