in my life i have had dogs, cats, birds, fish, hamsters, gerbils, guinea pig, and a rabbit.
dogs esp, but even cats require alot of maintenance and money(food, vets, cat litter, training). we ended up giving our dog to my father as we were in temp housing, and then moved, had a baby, with no fence. since the long time period, we felt bad taking her back as they fell in love with her. at the same time, our cat had to be put to sleep. to be honest, our life is much easier. with a toddler and new baby, the animals do require your time daily, and dogs demand attention as well.
rabbits, guinea pis, hamsters, ect require handling daily or they may bite or become timid. their pee smells so strong, the cage must be cleaned often. alot of rodents are noctyou can always get fish. you would be surprised how amazed children are with themurnal so may be loud at night. they do bite at times. they are small and can get hurt easily.
you yourself want a pet, than do it, but i wouldnt advise to get the pet now for the kids. they are young and will love it, but at the same time, often get bored at times just like with toys. and you will have to watch them at all times as kids dont mean to, but they arent aware how easy a pet can get hurt. and matter what you get, you will have to clean up more poop than you do now, lol.
that being said, a dog requires alot of work, but is the best pet you can have. they become part of your family. i would say that would be the best choice, but only after you do extensive research on temperaments. you have to find a breed good with kids, and a good breeder(dont go to a pet store). also, the bigger the dog, the more shedding, poop, vet and food bills, damage if chews, ect. and with dogs, you really cant leave them too long. cats would be second, i love cats and they are so easy to care for. its just some do and some dont like kids, you never know. good luck
eta- research turtles and salmonella, wouldnt do it