Having childen is one of the worst thing you can do for animals, even if you raise them vegan. Every child people bring into the world requires food, housing (both as a child and adult), medicine, education, toys, nappies, money, and a whole myriad of things. They are a consuming machine and will be consuming for 70+ years for most of them.
Your household waste increases, filling up landfills faster, causing methane production from said landfill. Polluting the environment around the landfill.
Encouraging diseases for scavenging animals who eat from the landfill which is a breeding ground for bacteria.
The toys will be made in factories polluting the atmosphere. Said toys will be mostly made of plastic and end up in a landfill when they are unfixable as they are not recyclable (Source).
The clothes too will require more farming of the materials (i.e. Cotton).
More land will be needed to grow crops to feed your brood and every other new child on this planet. This means more fields taken from the wildnerness and habitat destruction.
More land destroyed to build homes on to house these new people. More schools, hospitals, police stations, fire stations etc. More trees cut down to build these buildings (especially in places like America that have a weird obsession with wooden homes).
More medical research into disease that involves animal suffering in labs.
More gadgets built in labs overseas to keep them entertained.
Overall your carbon footprint will increase dramatically than a non breeder. (Source)
Simply put, just existing as we do now, humans kill animals inadvertently. So creating more humans will cause more killing.
Furthermore humans are overpopulated. We spay and neuter animals we deem overpopulated, why not ourselves? We adopt because of pet overpopulation, why not adopt because of human overpopulation? It's double standards.
Breeding is not a human right. Nor do you think about what the new human wanted. Suicide is one of the leading causes of death in the world. Why would you bring a human into a world just to be miserable? Why would you bring them into the world when you can pass on horrible illnesses? Why would you bring them into a world where abuse of humans and animals alike is rife?
A world where sexuality gets you killed or imprisoned. Where women are still seen as less than the male of the species. Where trillions of animals are killed yearly for pleasure. Where beheading is the norm. Where, if you're a boy in some countries your choices are usually kill or be killed. Where if you're a girl in some countries you're nothing more than a breeding machine. A world where mother nature is more erratic than ever thanks to humans (including you) continously producing more humans. A world where people are expected to slave away for pieces of paper or metal just to be able to eat and survive.
Why? Life is suffering. Life creates suffering.
If you want to reduce your harm of animals, don't breed more humans who's very existance will cause harm. And do go vegan.