Sounds like a dog starting to aproach maturity & is testing the boundries. The maturity process usually begins around the age of 2 & often runs until around 3. Might want to also run some blood work on the dog to rule out anything there.
I posted what I wrote below on a thread a while back & just copied it to here. It will give you some info on is most likely going on. But I would keep the dog away from the neighbor or school kids completely...for now. I would also keep the dog on a long line with you on the end around your own kids until you straighten things out. Very hard to Dx over the internet.
Some dogs coming up on mental maturity can be a rea PITA. Some just push a little here & a little there & others all out forget all the rules & realy have at ya & some are somewhere in between. Physical maturity & mental maturity are two different things. Physical maturity is when they reach their full stature & finish filling out. Mental maturity is when they reach their full capacity & attitude as as adult canine. They often become more serious, intense, more aware of their enviroment, intact males get alot more challenging to other males, especially, protective of 'property' which can be home turf & humans, just get 'forgetful' about rules & commands challenging authority etc etc etc. Most large breed dogs go thur this somewhere between 2 & 3 years old. Small breeds mature more quickly & go thru this sooner...haven't had small dogs in many years...but I think around a year or so give or take.
Different dogs & lines of dogs can be very different going thru this process....from your hardly noticing any change to out & out right handler aggression issues testing authority.
During this time you may need to reinforce all rules & even make a few new ones that require more absolute obedience & practice a NILIF(nothing in life is free)attitude if you don't already. Some dogs need to 'earn' everything from food to a pat of affection. Don't give a command that you can't inforce. Handler aggression issues need to be dealt with immediately, calmly & without emotion. Not going to go into dealing with this, as most people will not have this issue & if they do they need professional help, if not experienced & this is truly going on. It is not something to play with as you can get badly bittten if not handled correctly.
Most males are more ready to 'test' during this maturity stage then the females are. Althought there can be exceptions.
Most dogs just get pushy & test the rules & boundries. This process of maturing & testing can go on for weeks or months. Mostly he was a PITA.
My male constantly pushes & tests (but no his is NOT a dominant dog just s VERY pushy one). He was at his worse between 2 1/2 & 3 1/2 & became very HA at times. Mostly he was a PITA. My female would just 'turn a deaf ear' to commands & get pushy when she wanted affection & became more intense when protecting property.
When going thru this stage of your dog's growth you need to stay firm in your rules & be consistant in all that you do, because your dog will be watching for those inconsistancies & will be ready to take advantage when they happen.
You want to make clear to your dog that the rules are the rules & you as leader make those rules to be followed by all pack members(in multiple dogs homes) but you don't want to destroy your bond with your dog in the process.
Frmales as I said USUALLY don't go past the pushy I forgot all my commands stage, but some due. My female just got more demanding & more intense when working she challenged me a bit, but mostly nothing compared to my 2 males.
MY DOGS...MY RULES