First time I ever heard corn snakes need UVB lights. Corn snakes are active mostly at about dusk and near dawn, were most animals requiring uvb are active during the day. However there is some amount of UVB still around during dusk and dawn hours but giving the angle of the sun, the exposure on the ground would be very low so I don't really see cornsnakes getting much if any exposure to UVB rays.
On to the subject of the thread, I personally don't think a child under 8 should have a pet snake, supervised or otherwise. Young children can accidently hurt or drop a snake (and risk either injuring the snake in the fall or trying to catch it, or loosing it in the case of faster moving snakes, such as corn snakes). Ball pythons can move pretty quick when they decide to, though for the most part they move in a slow deliberate manner.
Personal views aside, I have to agree a ball python would be a better pet for a young child, as these snakes are slower moving for the most part, more 'girthier' which makes them a bit easier for children to hang onto than corn snakes.
However, corn snakes can be very docile and not move much while in hand as well. Baby corn snakes can be more nippy and tend to try and slither away if they do not feel comfortable in somebody's hands or feel threatened. But with regular handling they do calm down quite well and explore fairly slowly when held.
For children, they shouldn't be allowed to hold snakes for a long period of time as their attention spans are short. If anything distracts them they could wind up carrying the snake to some part of the house and putting it down, and forget about it (hence supervision is very important). Also, even when supervised if the adult is distracted (and yes, we do get distracted and forget we can't leave children unsupervised for a short period of time without something happening), and you may come back to the child doing something else and the snake nowhere in sight, or a crying child who lost the snake, was bit or the snake injured.
Of course the above may be not a concern with many children but not all children have the same patience, attention span, gentleness etc as others. Also, a year from now, they may have absolutely no interest in the snake. Thus I think the best thing is pick the snake you like, as you will be the primary care giver anyway, so you might as well get something you know you will enjoy for the entire lifespan of the snake (20 years or more).
Just my 2 cents worth, not trying to nay say anybody who has or wants to get snakes for young children, it is just something i wouldn't personally recommend. But then again there are a few children I have met that I feel would be responsible enough and careful enough not to misplace a pet snake or hurt it accidently. I have also met young children who I wouldn't trust a rubber snake with, much less a live one.
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PHLdyPayne