Here is what I found for if it does happen.
1. To purchase a gun in Illinois, you must first obtain a FOID card (Firearm Owner Identification Card through Illinois State Police. FOID requirements involve a criminal background check:
* Must be 21. Age 18-21 requires consent of qualified parent or guardian
* No felony convictions
* No drug addictions
* Has not been patient in mental hospital in preceding five years
* Does not have mental illness
* Must be a legal resident of U-S.
* Must be 21 to purchase handgun. 18 (with responsible adult permission) to purchase a long gun.
1. Waiting Period
* 72-hours for handgun
* 24-hours for rifle or handgun
2. Cities with Handgun Bans
* Chicago: Chicago bans possession, retail sales, and private sales and/or transfers of handguns and also bans the sale and/or transfer of certain types of handgun ammunition. It also requires that all other guns legally possessed be registered.
* Morton Grove, Evanston, Wilmette, and Oak Park also ban handgun possession.
* The following Illinois communities ban the sale or transfer of handguns: Deerfield, Elk Grove Village, Evanston, Forest Park, Highland Park, Morton Grove, Niles, Northbrook, Oak Park, River Grove, Westmont and Wilmette. Illinois is unique among states because of the number of communities with handgun bans.
3. Concealed Carry
* In Illinois, it is unlawful to carry or possess any firearm that is concealed in a vehicle or on a person. There are some exceptions: Licensed hunters, trappers, but they must transport their firearms in a non-functioning state (that is broken down, unloaded, in a case, not immediately accessible.)
4. Child Access
* It is unlawful for adults to leave their guns unlocked and accessible to children under the age of 14 (if that situation leads to injury or death with the firearm.)
5. Under Consideration
* Law that would limit handgun purchases to One-a-month. This has been proposed annually by Mayor Daley, and has never moved very far. The legislature is considering it again this session, but gun control advocates concede it probably won't get very far.
* The Illinois Senate has passed and the House is considering a bill that would ban the sale and manufacture of high capacity ammunition clips. The clips would be limited to 10 bullets, but those who currently possess high-capacity clips could keep them, and the governing of internet purchases is unclear.
Of course you don't know if this is just a BB gun or something else.
ETA:
Yes. Illinois law (720 ILCS 5/24-9) states "(a) Except as provided in subsection (c), it is unlawful for any person to store or leave, within premises under his or her control, a firearm if the person knows or has reason to believe that a minor under the age of 14 years who does not have a Firearm Owners Identification Card is likely to gain access to the firearm without the lawful permission of the minor's parent, guardian, or person having charge of the minor, and the minor causes death or great bodily harm with the firearm, unless the firearm is:
(1) secured by a device or mechanism, other than the firearm safety, designed to render a firearm temporarily inoperable; or
(2) placed in a securely locked box or container; or
(3) placed in some other location that a reasonable person would believe to be secure from a minor under the age of 14 years.
(b) Sentence. A person who violates this Section is guilty of a Class C misdemeanor and shall be fined not less than $1,000. A second or subsequent violation of this Section is a Class A misdemeanor.
(c) Subsection (a) does not apply:
(1) if the minor under 14 years of age gains access to a firearm and uses it in a lawful act of self-defense or defense of another; or
(2) to any firearm obtained by a minor under the age of 14 because of an unlawful entry of the premises by the minor or another person."
"Firearm" means any device, by whatever name known, which is designed to expel a projectile or projectiles by the action of an explosion, expansion of gas or escape of gas; excluding however:
(1) any pneumatic gun, spring gun, paint ball gun or B-B gun which either expels a single globular projectile not exceeding .18 inch in diameter and which has a maximum muzzle velocity of less than 700 feet per second or breakable paint balls containing washable marking colors;
(2) any device used exclusively for signalling or safety and required or recommended by the United States Coast Guard or the Interstate Commerce Commission;
(3) any device used exclusively for the firing of stud cartridges, explosive rivets or similar industrial ammunition; and
(4) an antique firearm (other than a machine-gun) which, although designed as a weapon, the Department of State Police finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector's item and is not likely to be used as a weapon.
****
