My daughter is 8 years old and I'm having the same problem. She always wants to come detect with Daddy. I've been doing some online research and the Gold Digger Metal Detector seems to be affordable and has good ratings . . . costs about $90.
"The Gold Digger is just the ticket for any entry level Gold prospector, relic hunter, coin shooter, and treasure hunter."
Features: 1/8" headphone jack and headphones included - Automatic tuning and ground balance - Power and sensitivity - Trash eliminator control to remove most undesirable items from detection - Treasure meter to determine strength of signal - Detects coin-sized objects up to 6" deep; larger objects up to 2 feet. - Requires two 9-volt Alkaline batteries (not included) - 1 year warranty.
Weight: 2.6 lbs, Adjustable Shaft: Yes, Assembled Length: Minimum 36"
Assembled Length: Maximum 46.6", Rechargable System Not Included
Batteries: 9 Volt x 2, Headphone Jack: 1/8", Arm Rest: Fixed,Arm Strap: N/A
Control Box Mount: Standard, Number of Frequencies: 1, Instr. Manual: Yes
Searchcoil Size: 7", Searchcoil Shape: Round, Searchcoil Build: Solid
Searchcoil Type: Concentric, Interchangeable Searchcoil: No
Waterproof Searchcoil: Yes, Submersible Searchcoil: Yes
Display Type: Analog, Number of Search Modes: 2
All Search Modes · Motion All Metal · Discrimination
Technology VLF Single Frequency, Discrimination: Adjustable
Threshold: Fixed, Sensitivity Adjustable
Ground Balancing: (Fixed) No, Ground Balancing: (Manual) No
Ground Balancing: (Automatic) Yes, Depth Indication: No
Pinpoint Mode: No, Volume: Fixed, Audio Tones: Yes
Number of Audio Tones: 2, Low Battery Warning: No
Good luck,
Dave