My kids aren't on grade level!! What do I do?
First of all, grade levels are simply an arbitrary norming system used by institutional educators, as a way of determining the skills and content taught to all children at a certain approximate age. These standards vary by jurisdiction (the standards in the US are not at all the same as the ones in the UK, and far different than the ones in China, for example). So "grade level" isn't really a good measurement of each child's abilities, and it is definitely not an indication of their intelligence.
That being said, it is not hard to "catch them up" to your local school's definition of grade level. Start where they are, and continue each day from there. Most children learn quickly and excel when given individualized attention. Plus, you'll be surprised how little time it takes to learn anything, when you don't have to wait for 25 other people to complete the assignment, pay attention, ask their questions, turn in their work, stand in line, etc.
Can I do this while .. pregnant/nursing/working/single/sick/disabled/your-unique-circumstance-here?
I have homeschooled (a school age child, not a preschooler) while pregnant, nursing, or both; with toddlers, newborns, or some combination thereof; working (from home and outside); while married, single and during a divorce; thru several moves, power outages (that lasted days), work being done on my home, blizzards and floods and tornado warnings; while battling depression, PTSD, infections, and other varied health issues; etc. I can safely say that if you are committed, you can do this.
The key is how committed you are. There are definitely times when I wonder if it wouldn't be easier to "just put them in school". There are definitely times when I'm tempted to call up the local school and sign up. But then I calm down, and realize that whether I educate at home or send them to school, I will still spend a good portion of time, energy and effort on making sure their education is the best it can be. It isn't actually any easier, just different.
How do I keep records or determine grades? Do they get a report card?
Keeping records and determining grades are two different things. You can keep a record by simply dating all completed work and keeping it. You can track using a journal or planner, taking pictures, making a portfolio, etc. Some jurisdictions require that you track attendance, subjects taught, work completed, show proof of learning somehow (through a portfolio, testing or evaluation), and those requirements may determine how you keep your records.
Grades are simply your determination, as the educator, of how well your students learned the content or skill you taught. You can figure out what kind of grade you want to make, from as simple as pass/fail (did they learn it or not), to how many correct out of how many questions (percentages/letter grades) to determining progress, to measuring effort. Many parents find letter grades or grade point averages superfluous, especially during the early years.
There are many systems available for you to help you keep records and determine grades. From paper planners to online trackers, there is a system that will suit your family.
How can I teach when ... I don't know it/didn't graduate/didn't do well/don't like it?
Studies show that homeschooled children do well regardless of the education level of their parents. So don't let your education (or lack of it) be a hindrance to homeschooling your children. If there is a particular subject you don't feel qualified to teach, there are many options, from learning with your children, to using an outside class or hiring a tutor. For most people, this doesn't even factor until you reach high school, and many options, from dual enrollment to community college to online classes to part time enrollment at your local high school, exist to help with that subject. If your child really wants to learn it, there will be a way for them to do so.
How do I tell family or friends? What if they criticize me?
How you tell those people important to you is up to you. You may choose to provide information, to simply and concisely say this is what you are doing, or not say anything at all.
The "mommy wars" are alive and well in homeschooling as well. Like many of your parenting choices that may or may not have been conventional, someone will have something to say. How did you handle the criticism you had about your child's name, the decision to breastfeed/bottle feed, your decisions in toilet training, the use of electronics, feeding them, bedtime, etc? It seems every single decision we as parents make is now subject to public opinion.
Please remember that these are your children. Your parents raised you already, now it's your turn. Your friends, chances are, don't live with you. It is up to you. You may need to stop discussing homeschooling with particular people, or even limit contact for a while. However, most people are supportive, especially after they see the results -- happy, curious, bright children who are learning!!