What is a normal blood sugar level for a 3 year old?

Ok Diabetes runs on both sides of our family. My husband was diagnosed 2 years ago. I never really noticed until the other day that he has been drinking and urinating more frequently. He has been this way for a few weeks now but I never notice it until recently. So today my 3 year old son ate 2 pop tarts 16 grams of sugar a piece and 1 juice box 15 grams of sugar in that. So all together he had 46 grams of sugar. After a half hour of eating and drinking that I tested his blood sugar level and it was 243. Is that normal for a 3 year old? He is not dehydrated, lethargic, does not have bed wetting problems. He has had a runny nose the last couple days but that's it. He acts normal. It's like I give him a gl of juice (sugar free) and then like 20 minutes later he is saying he is still thirsty and this goes on all day. I tell him to wait a little bit and then I'll give him more. Also he downs his drink within minutes like he can't get enough to drink. Am I just being a worried mother or is this something serious?