Metal detector for 8 year old

[Digaholic]

My son (8 years old) is starting to show an interest in metal detecting. I would like to get him his own detector (not a toy). I was considering the Garrett Ace 250, 350 or the Whites Coinmaster Pro. He will be hunting at the beach primarily, most likely in the dry sand and maybe a little in the wet sand. Can anyone provide any feedback or information on any of these machines? I am open to all comments or recommendations. Thank you.