Well, in a "formal way" it's "äiti" but we have many variatons for it.
For example there's "äippä", "mami" and "mamma" but those are more like in a cute or humorous way. The last one is also swedish. It's funny how you can hear 15-17 years-old teen girls call their mothers like that. Most of it is just family humor.
We don't have an exact mommy like the little children would call their mothers (a daddy we have. It is an "isi"). "Äiti" is the most used for children but you can hear other ways too. It depens where you are in Finland, South or North. Finland is wordy country.
There can be, of course, a "mutsi" but it's more like in slang the older teens use. You can't hear a little children say that or at least it's not in common.
Hope that helps.
For you is sinulle in Finnish.
How is miten in Finnish.
I am not Finnish. - (Minä) en ole suomalainen.
Finnish legend in Finnish is "suomalainen legenda".
Dot is piste in Finnish.
Queen is kuningatar in Finnish.
Dead is kuollut in Finnish.
Butcher is teurastaja in Finnish.
Slow is "hidas" in Finnish.
Library is kirjasto in Finnish.
Pie is piirakka in Finnish.
Wonderful is ihana in Finnish.