My son's adult teeth have started to come in, so his gums are a little itchy and painful.
ーMy son's adult teeth have started to come in, so his gums are a little itchy and painful.
「息子の大人の歯が生えてきたので、歯茎が痛痒い」
a little itchy and painful で「ちょっとかゆくて痛い」
もし赤ちゃんの乳歯が生えてくる場合は teething を使って次のように言えます。
ーMy baby has started teething, so she's a little bit grumpy these days.
「赤ちゃんの乳歯が生えてきているので、最近ちょっと機嫌が悪い」
ご参考まで!