How much should my toddler be eating?
Between ages one and five, a child's growth is in a decelerated stage; that is, they have slowed down in growth. Since growth slows down, their need for calories subsequently decreases, which in turn leads to a smaller quantity of food ingested per day. Added to the decelerated growth is a burgeoning independence which limits the variety of foods your child is willing to eat ("finicky eater"). Rest assured that toddlers do not need as much food as you might expect because of this slowing down of the growth rate. Three small meals and two snacks a day (and some will eat a good bit less) will probably be enough to fuel even the most active toddler. Please realize, too, that finicky eaters are the rule rather than the exception.
Some toddlers are eating very few solids, or even no solids, at 12 months. This is not unusual and really depends on your child - there is quite a big variation. We like to see breastmilk making up the majority (around 75%) of baby's diet at 12 months. Some babies will be taking more solids by 12 months, but others will still be exclusively or almost-exclusively breastfed at this point. It is normal for baby to keep breastmilk as the primary part of his diet up until 18 months or even longer. An example of a nice gradual increase in solids would be 25% solids at 12 months, 50% solids at 18 months, and 80% solids at 24 months.
Some children take a little longer to begin taking solids well. Some of them have food sensitivities and this may be their body's way of protecting them until their digestive system can handle more. Others are late teethers or have a lot of difficulty with teething pain. At this point there is NOTHING that your milk lacks that your child needs, with the possible exception of enough iron. As long as his iron levels are within acceptable levels and when he does eat you are offering him foods naturally rich in iron, then you have plenty of time before you need to worry about the amount of solids he's getting.
All you need to do is to continue to offer foods. Don't worry if he's not interested or takes very small amounts. Your only true responsibility is what you offer, when you offer it and how you offer it, not whether or not he eats it. That has to be up to him.
Trying to force, coax, or cajole your child into eating is never recommended. Continue to nurse on demand, day and night, and trust your child to increase the solids when he's ready. As baby slowly moves into eating more solids, your milk will fill any nutritional gaps nicely.