Your body will change and adapt very quickly to new exercise. Whether it is going to make you start ripping shirts in an incredible hulk style or not is questionable. Your shirts must have been close to tight before as you wouldn't change that much. Slightly noticeable yes but not drastic.

You are hungry as you are burning more calories. If you want to lose some podge then don't adjust your diet too much but if not then just eat some more carbs. the banana or potato are perfect.

I personally wouldn't have my 5 year old anywhere near weights so your right on that count.