My son is 3 everytime he get bit by a mosquito each bite swells ups what does that mean ther not jus a reg mosquito bite ther the size alil smaller th?

It is Normal.: What he is getting is called "localized reaction", which is quite common, this is not true allergic reaction.

Wheal: The bump left on the victim's skin after a mosquito bites is called a wheal, which is caused by histamines trying to fight off the protein left by the attacking insect. He may be having a reaction to the mosquito "saliva.".