זה מנהג ישן במשפחה שלנו, אבל גם הילדים אוהבים אותו.

but

Breakdown of זה מנהג ישן במשפחה שלנו, אבל גם הילדים אוהבים אותו.

• ב: in
• לאהוב: to like
• ישן: old

Questions & Answers about זה מנהג ישן במשפחה שלנו, אבל גם הילדים אוהבים אותו.

Why is there no word for is in the first part of the sentence?

In Hebrew, the verb to be is usually not written in the present tense.

So:

• זה מנהג ישן
  literally: this old custom
• natural English: This is an old custom

This is very normal in Hebrew. In present-tense sentences like X is Y, Hebrew often just puts the two parts next to each other, with no separate word for is.

But in past or future, Hebrew does use forms of to be, for example:

• זה היה מנהג ישן = This was an old custom
• זה יהיה מנהג ישן = This will be an old custom

What does זה mean here? Is it this or it?

Here זה means something like this or this is.

In this kind of sentence, זה often introduces or identifies something:

• זה ספר = This is a book
• זה מנהג ישן = This is an old custom

Depending on context, זה can also mean it, this, or even that in casual usage. But in this sentence, the most natural understanding is This is...

Also, זה is grammatically masculine singular, which fits מנהג because מנהג is a masculine noun.