Learn Hardcore Finnish: Lapsi jää lattialle paikalleen.

Dictionary form: jäädä = “to stay, to remain, to be left (somewhere / in some state)”
Here jää is 3rd person singular present: “(he/she/the child) stays / remains / is left”.

The noun jää (“ice”) is unrelated grammatically; it just happens to look the same. Context tells you whether it’s the verb or the noun:

Lapsi jää lattialle. – “The child stays/remains on the floor.”
Jäällä on paljon lunta. – “There is a lot of snow on the ice.” (here jäällä is “on the ice”, from the noun jää)

Why is it Lapsi jää and not something like Lapsi on?

olla = “to be”, a neutral statement of location or state.
jäädä = “to remain, to stay (behind), to end up staying” – it implies a change leading to a resulting state.

Lapsi on lattialla. – “The child is on the floor.” (just describing where)
Lapsi jää lattialle. – “The child stays/remains on the floor.”
→ He/she does not get up, does not go somewhere else, but stays there.

So jää here focuses on the idea that the child does not move away, but “remains” in that position.

What case is lattialle, and why not lattialla?

lattia = “floor”
lattialla = adessive case → “on the floor (location)”
lattialle = allative case → “onto / to the floor (direction / end point)”

With olla (to be), you’d normally use the adessive for a static location:

Lapsi on lattialla. – “The child is on the floor.”

With jäädä, Finnish often uses a “direction” case to describe the resulting location of a change of state:

Lapsi jää lattialle. – literally “The child remains to/on the floor,”
meaning: the child ends up and stays there on the floor.

So lattialle here encodes the idea of “ending up staying there (on the floor)”, not just “existing there”.

Could we say Lapsi jää lattialla instead? Would that be wrong?

Lapsi jää lattialla is not the usual or natural way to say this.

Lapsi jää lattialle is the normal expression: “The child stays on the floor / ends up staying on the floor.”
Lapsi on lattialla is fine for simple location: “The child is on the floor.”

Using jäädä with a pure static adessive (lattialla) is very unusual; native speakers expect a case that expresses end-point / result (allative -lle, sometimes illative -an/-en, etc.) with jäädä in this meaning.

What exactly does paikalleen mean, and how is it formed?

Paikalleen is built from:

paikka = “place”
paikalle = allative (“to the place”)
-en = 3rd person possessive suffix (variant expressing “his/her/its own”)

So:

paikalleen ≈ “to his/her/its (own) place”
In this common idiom jäädä paikalleen, it means “to stay where one is, to stop moving, to stay put.”

With a 3rd-person subject:

Lapsi jää paikalleen. – “The child stays where he/she is / stays put.”

Whose place is meant in paikalleen? Why is there a possessive ending?

The possessive ending -en refers back to the subject, so it means “the child’s own place / their own spot”.

Lapsi jää paikalleen.
Literally: “The child stays to his/her place.”
Idiomatically: “The child stays where he/she is, stays put.”

This is a typical way Finnish marks a reflexive sense (“one’s own place”) without a separate reflexive pronoun. The owner is understood from context (here, the subject lapsi).

Is there a difference between paikalle and paikalleen?

Yes:

paikalle = “to a place / to the place” (no owner indicated)
paikalleen = “to his/her/its own place / to their place (reflexive)”

Compare:

Mies juoksee paikalle. – “The man runs to the (scene / place).”
Mies jää paikalleen. – “The man stays where he is / stays put.”

In your sentence, paikalleen specifically ties the “place” to the child itself: the child stays in its own spot, not just “at some place”.

Why do we have both lattialle and paikalleen? Aren’t they saying the same thing?

They give different pieces of information:

lattialle → the physical surface / location: the floor.
paikalleen → the idea of not moving from one’s own spot: staying put.

Lapsi jää lattialle paikalleen. combines them:

The child remains on the floor (not getting up),
and specifically stays in the exact spot, not crawling or moving around.

If you say:

Lapsi jää lattialle. – The child stays/remains on the floor (but could still move around on the floor).
Lapsi jää paikalleen. – The child stays put where he/she is (location unspecified here).

Together, they make the picture more precise.

Can we change the word order, for example Lapsi jää paikalleen lattialle?

Yes, Finnish word order is flexible. Both are possible:

Lapsi jää lattialle paikalleen.
Lapsi jää paikalleen lattialle.

The basic meaning is the same. Very roughly:

Putting lattialle earlier can make the floor a more immediate part of the scene.
Putting paikalleen right after the verb may slightly highlight the “staying put” aspect.

But in everyday speech, both orders are fine and understood the same way here. The sentence doesn’t become ungrammatical; the nuance change is subtle.

How would this sentence change for the past tense?

Use the past form of jäädä: jäi (3rd person singular past).

Lapsi jäi lattialle paikalleen.
→ “The child stayed/remained on the floor, (right) where he/she was.”

Everything else (cases and endings) stays the same; only jää → jäi changes.

Is there a difference between jää lattialle paikalleen and using pysyy instead of jää?

Yes, there is a nuance difference:

jäädä (“to stay, to remain, to be left”) often implies that some earlier movement / possibility of change stops, and then the person ends up staying somewhere.
pysyä (“to stay, to remain”) focuses more on continuing in a state, without necessarily highlighting the moment of “ending up” there.

Compare:

Lapsi jää lattialle paikalleen.
→ Picture of the child not getting up, remaining on the floor, in that spot. There’s a sense of “ending up staying there”.
Lapsi pysyy lattialla paikallaan.
→ “The child stays on the floor, in place.”
Focus on continuity: the child keeps staying there over time.

Both are possible, but your original sentence with jää emphasizes the idea that the child does not move away but remains there as a result.