My kids are past the toddler stage now, but a favourite lunch for them was a mixture plate. This was just a mixture of whatever we had in the fridge! Maybe a bit of toast, some cold meat, some chunks of cheese, a pile of raisins, some apple or orange and a biscuit or a few crisps for after. They also liked soup with "dunkers" - either toast or sandwich.
Another favourite was toasties.
My kids are now 7 and 6 and eat a huge amount of food, they do however have a healthy diet and are very tall for their age and not overweight in the slightest. They are very active and obviously need the calories.
Toddlers should be always on the go, and need to eat regularly and until they are full. As long as they are eating healthy food, I wouldn't worry about how much they eat as long as they are not overweight.
Re the sugar free juice - I quite agree, i have now decided that sugar is no longer the enemy and that there are worse things in the sugar free varieties. I now give milk. water, watered down fruit juice or squash or high juice with sugar in it rather than sugar free. Rocks organic orange juice is very nice. I just make sure that they brush their teeth after meals.