Hi Leezel
We have a variety of snakes atm from a big 10ft very placid olive to a baby water python, and also have a 4yo daughter and 19mo son and our 4yo loves helping with the snakes and handling them, they are great pets for little ones as long as they know the rules, our daughter knows to wash her hands use the hand sanitiser gell, be very gentle, no quick movements etc
imo snakes are the best pets for kids they can learn so much from them, my daughter is as snake mad as we are. If your son thinks the spotted is too small have you looked at getting a older/bigger snake? I don't know the size or age of your spotted but we have three adult ones that are the perfect size for our daughter to hold, she even holds two at a time lol
The only snake she doesn't hold by herself is the olive as he is so big she needs help to hold him, and baby baby water as he is still kind of snappy but she holds the other eight snakes with a lot of confidence, more confidence then some of our friends who won't even go near our snakes lol
The best bit with getting another snake is that you already know how to look after them and the enclosure set up, maybe you could take your son with you to see what snake he likes and thinks is big enough that he won't hurt it.
Goodluck ion what ever reptile you choose!