(+ there are some questions to any Finn who decides to help out:)

The kid is in the bedroom. 

Makuuhuoneessa on lapsi. - Diphthong stem (huonee-) - GEN huoneen, ILL huoneseen, ESS huoneena etc. BUT: PART huonetta.

Also e.g.: "tuore" - fresh, new; "herne" - pea. (tuoreen, tuoressa, tuoreeseen, BUT tuoretta; herneen, herneesta, herneeseen, BUT hernettä)

The kids are in the bedroom.
Makuuhuoneessa on lapset. (or Lapset OVAT makuhuoneessa. If this is correct, then what makes the verb take different forms by the plural?)

There are three bikes in the yard.
Pihalla on kolme pyörää.

The bottle is on the table.
Pullo on pöydällä. (you may have confused it with "työ", which is usually used in plural (töitä, töissa etc.) The question is why työ is usually in plural and what would be the difference. Finns?:)

The bottles are on the table.
Pullot ovat pöydällä.

Tonight there is a finnish band playing.
Tänään soittaa suomalainen bändi.

Tonight there are finnish bands playing.
Tänään soittavat suomalaiset bändit.

My family owns two cars.
Perheeni omistaa kaksi auota.

My family has two cars.
Perheelläni on kaksi autoa. (posessive suffix is placed at the end; another diphthong-stem word; and not to forget about the vocal harmony:)

Do you want a crisp?
Haluatko sipsin? (if it is the particular one. or just one crisp. If that's any crisp of those that you have, and more likele that not just one, then: haluatko sipsiä?)

Do you want some crisps?
Haluatko sipsejä? (I don't believe there would be a difference in finnish, but I hope someone will tell us for sure:)