It’s best to avoid explaining or translating in Japanese when speaking English to small children.
You can say a sentence in English, and then say the same thing in Japanese. It’s not always a bad thing, but probably not necessary. Because they are under 5, they don’t need Japanese explanation. They are still young enough to learn a language naturally – the same way they learn Japanese. They do not need explanations the way that adults do.
When a parent speaks Japanese to their baby, there is nothing to translate.The baby has no choice but to understand. But after hearing words over and over, or using pictures or actions, they quickly understand the meaning.
Sometimes children don’t understand the first time, but that’s OK! Don’t worry.
They will get it after a few more times. If you say “Put on your shoes” they may not understand, but if you do the action and repeat it again several times during the week, they will understand. If you say “Get me the carrots” you don’t need to say “にんじん” just say “long, orange….” etc. Then say “carrots” again and point to carrots.
A problem with translating words is they will become dependent on it. As long as they say “わかんな～い！！” they know you will say the Japanese, and they don’t need to learn the English. Luckily, at 4 or 5 kids are learning fairly easy words – nouns you can point to in a store or book, verbs you can do the action. It’s more fun with no Japanese. And if they don’t understand – it’s OK!!