When I was a kid there was a company called spy tech. Honestly for most of my childhood they were the coolest thing ever! They had periscopes, big ears… ok that’s all I remember, but it was awesome! Now tech is sooo much better, and MUCH cheaper. With spy tools, chores become missions. Math becomes code-breaking. Your kid leaves you alone with you’re mimosa for hours.
Hidden camera:
Any camera is a great for natural science studies, go out in the woods and come back with pictures of plants, bugs and animals you can look up on the internets with them. “Mission” confirmations. “See mom, I did my chores.” And recording memories. There is something unique about a POV birthday party, people forget there is a camera and you really feel like you’re there. These specifically require but don’t come with a class 10 microSD card. If you don’t have one, be sure to remember to pick one up.
Can you imagine having real hidden camera glasses when you were a kid?! Come on, Mission Impossible!
These glasses are fit for adults, and maybe a little on the higher cost at over $50 with the required SD-Card (at the time of this writing) or maybe you want another option or the combo. Cheaper and comes with an SD-Card.
Invisible Ink:
Plan a spot where you exchange messages. Curled up in an old cologne bottle. Tucked into a book. Or you can go really crazy and make a fake outlet or light switch compartment. When I was a kid, I’d screw out the deodorant when it got low and hide things under there (I once almost threw out $10 I hid under my deodorant). Or with this pen, you can exchange messages right out in the open. Write, “pick up milk” on a stick note in regular pen, and, “You’re mission, should you choose to accept it. Remove all DNA and incriminating evidence from the dishes from last nights gala. Send confirmation.” So the kid, washes the dishes and sends you a picture.
Invisible Ink Marker with Metal Arachnid Mini LED Blacklight
This book is widely considered the standard book of cryptography for kids. They have codes of differing difficulty. Exchanging messages, written in UV invisible ink, hidden in the toilet paper roll, written in code, will make your kid feel like a true spy… of course then you’ve got to write in code… the things we do for our kids, its worth it.
I spent a lot of time looking for a decent periscope, they were either over priced toy crap or over priced professional crap, either way, not my bag of tea… I drink coffee. Then I realized what I was trying to do, I just need a way to look around corners. Really a cellphone camera would work, so if you’ve got an old cellphone with a busted screen, put clear box tape over the glass and give it to your kid. Older smartphones are also really very cheap as well, you don’t need a sim card to use them like an iPod Touch so if you want to keep them off the internet, you can just not give them the WiFi password… your WiFi IS password protected right? Not password1234? Really I guessed it from across the internet?! Stop reading right now and go fix that! (Statistically someones going to have that password and then this will pay off, it will be hilarious! But I probably will never know, that’s what imagination is for.) Phew, I digress. Here is a list of cheap smartphones on eBay. Filter by your carrier with options on the left if you want to put cell service on it, most carriers have cheap pay-as-you-go options.
This toy kinda violates my principles… because it actually IS a crappy toy. The microphone is not in the right place for a parabolic mic, and there are SO MANY lost educational opportunities there to discuss the focusing power of a parabola 
When I was a kid, the coolest spy device, in Get Smart and the back of catalogs, was the review mirror glasses. Cheap, and according to the reviews, legitimately functional even for adults (perhaps better for adults due to fit), one of my childhood favorites in a higher quality form factor.
Every spy needs a way to track their target. The locator I had listed was some SUPER cheap crap. The problem is the next option up is $15 and has reviews almost as bad. 
Walkie-talkie?! This is 20 effin 20 baby. (currently, right now, as I write this… its likely not as you read this so adjust date accordingly). You could get some FRS radios, which ARE awesome! This cheap little cellphone is perfect for a teen. Don’t want to pay for a cellphone bill, skype works fine within range of the wifi router. Don’t expect fast mobile data, you can expect dial up speed data on this phone, but for a kid with a data plan, that’s EXACTLY what you want to avoid unexpected overages. This phone is Tracfone locked, but Tracfone is cheap pay-per-minute so it could be a good provider for a kid, and for this price it also just makes a good camera/MP3 player/WiFi messenger/Skype phone.
While looking for a better bluetooth tracker I ran across this. I know cheap tech can get absurdly cheap, but $15 for a smartwatch? The worse/best part is, this isn’t the cheapest one, if you don’t want the camera you can get one for $10, check the “also bought” category in the link below to delve into a plethora of ridiculously cheap smartwatches. Most of them only work with Android and I have no idea how well its features work. I’ll see if I can find someone to review it for it’s kid spy (kid tracking) applications. If you wanna be a creeper parent, there’s a watch for that too.
You don’t want to leave your spy out in the field without enough film! … eh… er… memory. WARNING REMINISCING COMMENCING!!! I remember my first gigabyte hard drive, 1.6 gb, $100’s, cha-ching! The year before I saw my first flash memory in a catalog, 1gb, $999, but only the size of a stack a credit cards, sooo small!!! SOOO SPY!!! I thought. HAHAHAHAHA!
You don’t need anything fancy, but memory is so cheap you might as well go a little overkill. I can’t imaging your kid using more than 32gb of memory (that’s what I thought with 1.6gb back in 1995), so unless you have a hot neighbor who has a habit of changing in front of windows, that should be more than enough. These are small enough to hide in the best of spy tradition.
(Remember: I’m not your kids parent, I can’t be held liable for anyway your use or misuse of this information. I can’t be held liable for how this information affects your kid, your dog, your, house flies or your shoelaces. I am not responsible for any offense you decide to feel in responce to reading this information. Live responsibly.)
Radical Kids Toys 