My 3 year old (diagnosed last Oct when 2 and a half) rarely shows any symptoms of a hypo and quite often can drop into the 2's and just complain of feeling a bit tired - although she sometimes says her tummy is hurting and this is a sure sign that she is low. We try and keep her around 5 - 7 but it is so hard when they are this small. I find our daily BG readings can fluctuate quite a lot but then her 3 month HBAc has still remained really good, around 6.5 - 7 so the hospital are really pleased. I agree with leggott that they seem to feel tired if their blood drops really quickly, for instance I've noticed that Sylvie's BG drops quite suddenly late morning and even if it only drops to 6 or 7 then she will feel the effect.
We recently went on holiday and found she had more hypos than usual, despite trying to keep to the usual routine as much as possible. I think it was due to more activity and excitement than usual...we also had quite a few highs which could be put down to the rebound after the hypos plus a few extra treats such as ice creams etc, very hard to avoid while on holiday and they must have some fun! We tried carb counting for the first time while on holiday but it was a disaster due to all of this so we are starting on that now and hoping that it will improve control.