they are afraid of something
Mark
He is afraid you don't feel all the love he has for you because he is always working and barely has any time for you. You would notice something's going on and once he explained you watched a movie/cartoon and cuddled
Renjun
He is extremely worried about your health and all he wants is for you to be healthy. He would do anything for you. This sweetheart tried making you feel better by feeding you and cuddling you. He's scared because lately you've been getting sick a lot more than usual.
Jeno
He is afraid of losing you. You mean soo much to him and he can't imagine living without you. He spends soo much time with you and he really cares about you. You know how much this adorable little mess tries and you love him for it.
Haechan
Haechan knows how to be a complete savage and he knows how to make people cry. He knows your weak spots and he wouldn't use them unless you got into a big fight but he still loves you and he doesn't want to hurt you or make you feel insecure.
Jaemin
He is afraid someone will hurt you and he won't be there to protect you. It's cute how he cares about your safety. He tries to spend more time with you and he is treating you like his princess. He doesn't want to see you hurting because it's hurting him even worse.
Chenle
He is afraid you don't love him because he's too clingy. He will try to be less clingy and you thought he's sick or dying. You love him for his clinginess and you think it's adorably cute but you don't want him to change because he's just right.
Jisung
He is afraid of love at such a young age. This cutie never felt this feeling and he's pretty confused about it. He would ask his hyungs for help. He would try to be closer to you until one day he asked you to be his girlfriend in school. This little fluff ball would be soo in love with you once he knew what love is but he would still be afraid of being hurt so he wouldn't show exactly how much he loves you.
(Next; you teaching them words in your language)