In most states, this can be fine. It needs no formal language, it needs no formal typing. It needs nothing special except:
1. It must state a present intent that you intend to dispose of your estate as set forth in the document.
2. You should recite that you are of sound mind and body and intend the document to be your last will and testament.
3. It should be witnessed by two people, who sign twice. First, they sign with a statement that they saw you sign the document; second, they sign again with a statement saying that you are of sound mind, and expressed a "testamentary intent" when executing the document (That you knew you were signing a last will and testament.
CAVEAT: this is not legal advice, and as always, you should consult an attorney licensed in your state. SOME states require THREE witnesses; SOME states also require that the document be notarized (or used to).
So, if you want to be very very safe, you should consider taking the piece of paper and three friends (who are NOT BENEFICIARIES and NOT THE PROPOSED EXECUTOR OF YOUR ESTATE [you need them to be disinterested], trek down to the bank, and have all three sign it, and have the document notarized.
Finally -- there are will kits available on the interent that will probably meet your needs, either free or at low cost ($20??) on line. There are also forms and books at your library. These are worth looking at.
With regard to your children -- statements as to proposed guardians will be ... considered, but are not dispositive -- the court would consider the best interest of the children over your desires.