The responsibility of any animal is the adult's, not the child's.
Many parents say they want to get a pet to teach their children to be responsible. What frequently happens is that the child loses interest and the animal suffers, and the child may resent the animal for the nagging they get from an adult.
Often the pet is given away becuse "you didn't take care of it". The child has learnt that life is disposable and that if they wait long enough, someone else will relieve them of the responsibility.
Let your children help with pets, but don't insist. Small children enjoy caring for a pet as something they can do together with the parents. The more interest you show the more enthusiastic they are likely to be. So if the children appear interested, encourage them.
They will learn most from watching your actions and the tone of your voice, from this they'll learn about waiting patiently, caring and enjoying a living creature for what it is and not what you want it to be.
When parents find solutions, rather than dispose of an animal for convenience sake, an important concept is communicated to the child. Either way, you must reconcile yourself to the fact that an animal is an adult's responsibility.
It is unreasonable to expect a child of any age to take sole responsibility for the care of any pet. The pet and your children, as well as the family peace, will greatly benefit from you accepting this.
Unless you are enthusiastic, informed and committed about what is involved in owning a pet - a stuffed toy is a better choice!