Pushchairs/strollers or whatever you choose to call them are used for pushing your baby/ tot in. The dogs then walk alongside such push chairs.

the OP is clearly doing this for advertisement, but while we're on the topic, i don't think they're very good for your dogs.
if your dog is too ill or old, go for a shorter/slower walk and if you want to go jogging, leave the poor old/sick dog at home who can't keep up with you.

My mum's dog suffers from really bad arthiritis (he walks like John Wayne!) and so my Mum bought him a stroller. He hates being left out so now he gets to go with them when they go for a walk... It's not ideal but hey, sometimes life isn't.