Дети любят клеить наклейки в альбом после урока.

After любить when you mean to like/love doing something, Russian normally uses the infinitive:

Дети любят клеить наклейки = Children like sticking stickers

Клеят means they stick/glue, so Дети любят клеят... would be ungrammatical.

Клеить is imperfective, which is the normal choice after любить when talking about a general habit or activity.

• любят клеить = they like doing this activity in general
• любят приклеить would sound wrong in this context

Russian usually prefers the imperfective after verbs like любить, нравиться, начинать, when the focus is on the process or repeated activity.

Here наклейки is in the accusative plural, because it is the direct object of клеить.

The dictionary form is also наклейки for the nominative plural, so the form looks the same.

That happens because наклейка is inanimate. In Russian, for many inanimate nouns:

• nominative plural = accusative plural

So:

• наклейки = stickers, as the subject
• наклейки = stickers, as the direct object

The role is understood from the sentence structure.

Because в альбом shows direction/destination: the stickers are being put into the album.

With в:

• в + accusative = movement into / toward something
• в + prepositional = location inside something

So:

• клеить наклейки в альбом = stick stickers into the album
• наклейки в альбоме = stickers in the album

This is the same basic contrast as:

• идти в школу = go to school
• быть в школе = be at school

Because после always takes the genitive case.

The noun урок becomes урока in the genitive singular:

• nominative: урок
• genitive: урока

So:

• после урока = after the lesson / after class

This is a fixed rule with после.

It can mean either, depending on context.

Most literally, урок is lesson/class period, so после урока means after the lesson or after class.

In real usage, it can sometimes be understood more generally as after class if the situation is clear. If you wanted to say after lessons/classes more explicitly, you might also hear:

• после уроков = after classes / after school

So this sentence could be about children doing this after a particular class, or just as a general school-time activity, depending on context.

The singular just means into an album / into the album. Russian has no articles, so альбом can mean:

• an album
• the album

depending on context.

It does not have to mean only one specific album in an overly strict way; it can also be a general idea: children like putting stickers into an album.

If you wanted plural, you would say something like в альбомы, but that would mean into albums.

No, Russian word order is fairly flexible. This sentence has a very normal, neutral order:

Дети любят клеить наклейки в альбом после урока.

But other orders are possible if you want to emphasize something different. For example:

• После урока дети любят клеить наклейки в альбом.
  Emphasizes after class
• Наклейки дети любят клеить в альбом после урока.
  Emphasizes stickers

The original version is the most straightforward and natural neutral order.

Yes, but in Russian клеить наклейки is still a normal and natural expression.

Literally, клеить means to glue / stick, and with наклейки it means to put stickers on / to stick stickers.

So even though stickers are self-adhesive, Russian still commonly uses клеить for the action.

Because в альбом means the stickers go into the album, usually onto pages inside it.

If you said на альбом, that would usually mean onto the album as a surface, for example onto the cover.

So:

• в альбом = into the album
• на альбом = onto the album

For a sticker album, в альбом is the natural choice.

They are:

• дети → dictionary form: ребёнок; дети is the irregular plural children
• любят → любить = to love, like
• клеить = to glue, stick
• наклейки → наклейка = sticker
• альбом = album
• после = after
• урока → урок = lesson, class

A useful thing to notice is that дети is not formed regularly from ребёнок. It is an irregular plural that you simply need to learn.