Teeth grinding among toddlers and young children is common and in most cases occurs during sleep at naptime and bedtime. Most children will grow out of it by the age of six. Because most cases of tooth grinding occur before the child has their adult teeth, it usually does not cause any long-term damage.
In some cases, kids may grind because the top and bottom teeth aren’t aligned properly. Others do it as a response to pain, such as from an earache or teething. Kids might grind their teeth as a way to ease the pain, just as they might rub a sore muscle. Many kids outgrow these fairly common causes for grinding.
I may be good to have it checed by the GP to rule out any ear infections.
Does it occur for years and does it have your concerns than it may be good to have it checked by a child dentist.

I would get it checked. Teeth grinding can also be a sign of a case of worms.

Possibly something that will cause deterioration if she does continue when she has adult teeth :/

Mine are more likely to grind if worrying about something or if they have worms

We took our daughter to the dentist too and they said all is OK. Phew.

We have a teeth grinder in our house too!!

I am so glad I read this. My 4yr old son has also just started to grind his teeth in his sleep. This post has eased my mind x

My 4 year old son does this to, we contacted the dentist as we were a bit worried but he said at this age I shouldn’t worry.

I’m not sure about a toddler but my 9 month old has her bottom 2 & has just got one come through up the top & is grinding hers

I’m wondering the same thing, ours are only 1 with only a few teeth but I worry that it may be doing damage! I manage to distract them from doing it during the day by clicking my tongue which they then copy and start doing but I think speaking to a dentist will be my next course of action just to be sure….

My middle daughter did this and it was so noisy.
It was also bad from a dental point of view once her adult teeth came in. She ground her teeth down.
You can talk to a dentist about this and see what they think. Most likely nothing will be done but if hes still doing it when his adult teeth come in then he might need teeth guards to protect his teeth.

Why does my child grind her teeth?
Experts don’t know for sure what causes teeth grinding (or bruxism, as dentists call it), but they point fingers at tension or anxiety, pain (from earaches or teething, for example), and malocclusion (a dental term for when the teeth don’t line up just right.) Some also suggest that breathing problems – from a stuffy nose or allergies – may play a role. And there’s some evidence that pinworms are sometimes the culprit.

Finally, your child may just be getting used to the sensation of having teeth in her mouth. Teeth grinding isn’t uncommon among babies who are getting their first teeth, beginning at around 5 or 6 months of age. It’s also common among children who are starting to get their permanent teeth, at around 6 years of age.
About 38 percent of children grind their teeth. The average age for starting the habit is around 3 1/2 years, and the average age for stopping is 6 – though, of course, people of all ages grind their teeth.

Your child is a bit more likely to grind her teeth if you do. She’s also more likely to grind her teeth if she drools or talks in her sleep. Almost all teeth grinding happens at night, though some kids do it during the day, too.
Is teeth grinding bad for my child?
In most cases, teeth grinding sounds worse than it is. It’s very likely that your child isn’t doing any damage to his teeth and he’ll soon outgrow the habit.

Mention your child’s grinding to his dentist, though, so she can check his teeth for wear and any resulting problems, like pulp exposure, cavities, or fractures. Also have your child checked if he complains of pain in his face or jaw during the day, because this can be a result of zealous teeth grinding.
Can I do anything to help her stop?
Although the sound can be disconcerting, you’ll probably just have to wait for your child to grow out of the habit. In the meantime, it won’t hurt to work on a soothing bedtime routine – maybe a leisurely soak in the tub, a little back rub, soothing music, or extra cuddling in the rocking chair.
If your child is teething or has an ear infection, ask your doctor about giving her the proper dose of acetaminophen or (if she’s 6 months or older) ibuprofen to ease the discomfort.
Some moms of babies report that they offer their little ones a pacifier when they start grinding their chicklets. (It may not stop the grinding, but they prefer listening to the squeak of a pacifier than teeth grinding together.)
If there’s a problem with the way your child’s teeth are lining up, the dentist may be able to polish them to fit together better. Older children who grind regularly are sometimes fitted with a night guard – a plastic device fitted to the mouth to prevent clenching and grinding of the teeth during sleep. But your child’s dentist probably won’t consider this until your child has at least some permanent teeth, around age 5 or so.

This is from google, you may like to check more sites for yourself : just google: my three year old grinds teeth in sleep.
My advice is to check with a dentist as early visits to the dentist helps the child later on. The dentist can just start by having the child sit on your knee and getting them used to opening their mouth. And with the grinding issue will provide you with help and advice, will put your mind at ease. Good Luck