A.,
Children will determine for themselves how much they want, however, I strongly caution you against the juice!
If you feel the need for juice cut 100% pure not from concentrate orange juice in half with water.
It is important that they not get a sweet tooth this early for many reasons.
1) Behavior - sugar is the biggest mood changer you can give
2) Tooth & Gum Health - it is pure sugar attaching itself to your son's teeth and will cause tooth decay quickly
3) Taste - If he associates sweet with liquids you will raise a child that won't drink plain water.
Set a good example and keep a glass of water with you all the time and have that be the only thing he see's you drink.
Children do as their parents do. If you drink anything other than water then so will he.
I have raised three children and the only time they juice was when they were much older 4-5 years in a glass on a Sunday breakfast.
I just didn't and don't buy it.
We drink coffee in the morning (not the kids)
Water the rest of the day
Wine occaisionally (not the kids)
Milk in cereal
Herb Tea
Not only will this save you tons of money on your grocery store, but will also save you dental bills, and prevent childhood obesity.
If you look at the calorie count on a glass of juice that turns to straight sugar as compared to so many other foods it is really such empty calories that will only serve to make you son a sugar junkie.
Regarding the foods he eats, do an assessment of what food group they are from.
Are they sweet vegetables, or leafy green vegetables?
Make sure he's not getting too many carbs as they will immediatley turn to sugar as well.
At his age if you hold him in your lap at the table he will naturally reach for things on your plate. Let him.
Smash up what he wants and let him explore the textures and flavors, and offer baby foods that are not sugar based.
(corn peas carrots sweet potatos)
Since your breastmilk is sweet when he wants something sweet he will go more for your breast to get his sweets.
Additionally as you know it has every single nutrient he needs, so you won't have to worry he is missing something.
Remove the stumbling blocks, eat healthy yourself, and set a good example on beverage choices.
Good Luck!