Should we have an attorney if my son cut his foot on glass at a restaurant and he severed an artery and all 5 tendons in his foot and had to have 2 surgeries to repair the damage?

I am sorry to hear about your son's injury. You or he, if he is 18 or older, may well have a valid lawsuit against the restaurant but there simply is not enough information here to determine that.  Broadly speaking, every personal injury lawsuit requires that you prove 2 things - that the other party did something (or failed to do something) wrong and thus are liable and second, IF they are liable, then you have to prove with some reasonable certainty the amount you were damaged.  Here it sounds as if you have no problem establishing he was damaged and can, with the help of an attorney and/or doctors, establish a reasonable amount of those damages.  So the question comes down to can you prove the restaurant did something wrong and is liable?  Either way, that is likely to take the assistance of an attorney experienced in personal injury lawsuits to be able to properly evaluate whether you can prove it, and if so, then how much your damages are.  Even then, you still will need someone familiar with the system to present your claim to the restaurant and/or their insurance company and potentially to file a lawsuit to seek the full amount you are entitled to recover.  You will be at a severe disadvantage if you try to do this yourself without the help of an attorney - it is, afterall, what they do for a living.  The other side, or their insurance company, will have knowledgable legal staff working the matter.  You should too or you will most likely be taken advantage of.  Remember, no matter how "nice" the other side may be, their job and what they are being paid to do is to minimize the amount they have to pay you.  They will NOT look out for your best interest and you should NOT take your legal advice from them.  Good luck.