Hello David. It is ok you say in this way. But if you say "晚安两只熊猫，睡个好觉！",this is better . 晚上好 means good evening , but 晚安 means good night. Kids learn foreign languages very fast. If you often talk to them in a foreign language , they can easily understand the language. My daughter is only 6 years old, but my wife and I often talk to her in English and we often ask her to watch English cartoon movies(of course she likes English cartoon movies very much).She also likes English songs very much. She can sings the songs like " you are my sunshine, Do-re-mi" and she is trying to learn 'let it go". Now she can understand a lot of English and sometimes she also speaks some English.

Another way to say 睡个好觉: 好好休息hǎohao xiūxi,rest well.休息 means to rest. There is a sweet way for your son to remember 晚安wǎn'ān better since you son has already learned "我爱你".The Pinyin without the tone marks for 晚安 is w a n a n. If you make every individual alphabet a component of another word's Pinyin , it could be wo ai ni ai ni. Let's add the tone marks and make a small change, you will see it as wǒ ài nǐ, ài nǐ我爱你,爱你 meaning "I love you, love you." Doesn't it make 晚安 a very sweet word to say to your beloved ones? You can tell your son about this that whenever he hears 晚安 from you, he can relate it to "我爱你爱你" which shows your love for him. Don't get me wrong though, 晚安 doesn't mean 我爱你爱你 culturally. Hope you like my answer.

"晚上好，两只熊猫。睡个好觉！“ "晚上好，大象。睡个好觉！” “晚上好，老虎。。。” commas are necessary here...

"晚上好, 两只熊猫。睡个好觉！“ "晚上好, 大象。睡个好觉！” “晚上好, 老虎。。。” "晚安，两只熊猫。睡个好觉！“ "晚安， 大象。睡个好觉！” “晚安，老虎。。。” Punctuation matters:-)

If you mean 'Good night, two pandas. Have a good sleep' then you should change "晚上好两只熊猫。睡个好觉wǎnshàng hǎo liǎngzhī xióngmāo. shuì gè hǎjiào" to “晚安熊猫们。睡个好觉wǎn'ān xióngmāomen. shuì gè hǎjiào”, the same with "晚上好大象。睡个好觉” and“晚上好老虎” , changing them to "晚安大象。睡个好觉wǎn'ān dàxiàng.shuì gè hǎojiào"“晚安老虎......wǎn'ān lǎohú”"你关灯吧" is correct for "turn out the light". Let me explain: 1.晚上好means good evening while 晚安means good night, a wish used in evening time to someone going to bed. The same as 午安wǔ'ān，a wish used to someone who is about to take a noon nap. 安 means peace. You might think 早安zǎoān is used to wish someone who is about to take a morning nap. The answer is no. 早安is Taiwanese way to say 早上好 zǎoshàng hǎo meaning good morning. Mainlanders don't say 早安to mean 早上好or 上午好shàngwǔ hǎo. 2. 晚安is a wish you said in a conversation. It is weird when you say the numbers of the people who get your wish. For example, I have two friends. I will not say "Good night, two friends." I would rather say "Good night, friends!"“晚安，朋友们！wǎn'ān，péngyoumen”Same here, you say "Good night pandas" rather than "Good night two pandas." 们men makes 熊猫and 朋友a plural form. To be continued.