When your child has an articulation disorder when they are very young, you may thinks it's cute or sweet when they say "wabbit" or "thweet" but once your child starts grade school, having an articulation disorder can become very difficult for them. He or she might get teased at school, or people might think they are younger, or less intelligent then they really are.
The first step to helping your child is to find a Speech Therapist, and the earlier the better! Don't let an articulation disorder become a habit that's difficult to break. In most cases your therapist can easily correct R or S misarticulations in a few short years and by the time your child leaves grade school, they will be speaking clearly and correctly.
If for some reason your child isn't making progress, there may be a more serious underlying neurological disorder, such as Childhood Apraxia of Speech, and further evaluations should be conducted.
What can you do at home? There are a lot of things you can do. First, ask your Speech Therapist how you can support your child at home, they know what your child is able to do or not.
If you child cannot produce an R or S (or any target sound), then expecting them to do it at home is unrealistic. However, you can start to draw your child's attention to the correct pronunciation of a word in a gentile way. For example, if they say, "what a cute wabbit!" you can say, "yes, that's such a cute rrrabit." Emphasizing the R will draw attention to how the word should sound. Don't do this with every incorrect sound, but just enough to help your child start to hear the difference.
If you child can produce an R or S, but only as an individual sound, then setting aside a few minutes a day, even just 5-10 minutes to practice repeating the sound correctly can make a big difference. Be careful! Don't let your child practice the sound incorrectly! That will just form another bad habit they will have to change. If your child isn't making the perfect sound 70% of the time or more, then stop practicing and wait until the Speech Therapist has taught them how to produce the sound correctly.
If your child can produce the sound and is working on using the sound in words don't overwhelm your child by correcting every error they make when speaking. Pick a time during the day, maybe it's during a meal, or when you're driving in the car, or any random 10-20 minutes where you practice a list of words that contain the target sound. Some things to keep in mind, it's much more difficult to use the target sound when using sentences instead of words and the target sound (especially R) can be more difficult to produce in certain sound combinations within words themselves. For example, it's much easier to say "ear" than "girl." Your Speech Therapist should be able to give you a list of words to work on that are appropriate for your child. If your child can say "ear" and the R sounds perfect, it's better to have them repeat that word 10 times with the perfect R, than having them say "girl" incorrectly.
If you child is able to say the sound in words and even sentences and is now trying to remember to use their new skill during everyday conversation, then congratulations! You are on the home stretch, and your child is getting close to achieving their goal. Keep in mind that forming a new habit is difficult, and they may not always remember to use their target sound, especially if they are tired or excited. Pick a time of day where you expect your child to use the correct sound and then have times when they can just let go and not have to worry about it.
Learning to say a sound correctly and breaking the habit of saying it incorrectly takes time, but with the help of a Speech Therapist and a supportive family, it can be done!