My normally calm puppy barks at people who are on a bike, children pushing a toy...?

We have a 20 week old Mastiff/German Shepherd mix. She is very sweet and calm. She is great with other dogs and kids. However, when she sees someone doing something like riding a bike, pushing a push toy, hula hooping, riding a scooter... she gets a little freaked out and starts barking, like the object is hurting the person and she needs to protect them from the object (bike, scooter, toy...). Any ideas of how to stop this behavior? She is fine with the objects alone, but once someone is using it, she starts barking?

It is because the constant movement of the object confuses her. When she is doing this, just give her a quick correction, like a tap to the neck and say "EH!" Don't do it in an angry way or a funny way, just an unemotional way. Then walk away. Show her that the movement is nothing to be afraid or confused about and the correction will get her to stop and calm down.

anything new will make your puppy excited just give her time to adjust

Try using some of these objects yourself at home to get her used to them. My dog used to be the same with pushchairs and bikes but soon got used to them.

she is still a puppy and i don't think she has ever seen any of the objects yet. I think after a while she will get used to it.

Most dogs bark at things if they don't know what they are. Carry her over to whatever she's barking at to show her that it's nothing.

She probably does think it's hurting them. Or she gets the human smell and has no clue what those crazy round things are, or why the human smell is moving so fast.

Get your bike, hold her on her leash and get on the bike. Don't use the pedals but walk to the bike with her. Do the same thing for the other stuff she gets nervous about.

She just needs to be shown what they are and that they are OK.

she is doing her job. she is protecting you and letting you know someone is there.