Is diet coke better than sugared sodas, if soda is given to children?

Yes. It is better to avoid soda altogether. But diet soda would be preferred.
Diet soda??? Corn syrup or asparmate? Pick your poison.The fda has ruled that the sweetener in diet drinks asparmate is safe for consumption at current doses in drinks...Uhmmm asparmate breaks dwon into methanol under extreme acidic or alkalinic conditions.Don't believe the fear mongering in the internet, but as long as there is water, milk and natural fruit juices, the choice is pretty clear.
Neither are good. Unfortunately, the quest to give us a sweetness fix without calories may actually be worse than natural sugar. If you want to program your baby's brain to crave sweets, and then battle that craving for life, offer it often in any form.That may be why so many kids now face obesity even before school age. I favor never using food or sweats as a reward. You may regret the long term effect.
Both not too good. Diet coke has aspartame, coke has sugar. Neither are good for children's diets. Stick to milk, water, and juices if you can.