Is it nessesary to give injectable polio vaccine to a child in the u.S.?

Yes. Except for smallpox, every preventable infection made a comeback once immunization rates dropped.
Only form available. This is the only form of the vaccine that is available to practitioners in the US. As long as there is international air travel, an infected carrier by the polio virus could be in your mall or supermarket the day after they arrive from an endemic area of the world. As long as such areas exist, we must keep vaccination rates up or it will return.
Yes. As a doctor, father and grandfather, it is vital to immunize properly. There is no rationale reason to avoid vaccinations in mostly every situation.