I'm going to take a shot here because it sounds very similar to Don't Be Afraid of the Dark (2010) in which a little girl and the family battle black creatures from the basement, the "Tooth Fairies".
In flashbacks of previous families there were other children, multiple children which is what you may be recalling.
At Blackwood Manor in Providence County, Rhode Island, renowned
wildlife painter Lord Blackwood summons his housekeeper into the
basement where he reluctantly kills her with a hammer and chisel. He
removes her teeth, as well as his own, and offers them to mysterious
creatures down an ash pit within an old fireplace; however, the
creatures demand the teeth of children. Blackwood begs for them to
give back his kidnapped son, only to be dragged down the ash pit by
the creatures. In the present day, 8-year old Sally Hurst arrives in
Rhode Island to live with her father Alex and his girlfriend Kim, both
restoring Blackwood Manor to put it on the market for their client Mr.
Jacoby. Sally is depressed due to her mother forcefully putting her in
Alex's care and giving her copious amounts of Adderall. On the first
night of her stay, the melodious tune from a carousel-styled
nightlight awakens the creatures in the ash pit. The next day, Sally
wanders the grounds and finds the hidden basement's skylight. One of
the workmen restoring the house, Mr. Harris, warns her, Alex and Kim
not to venture into the basement, although they do regardless. Sally
takes interest in the sealed fireplace where she hears the creatures
calling her name and follows the mysterious voices. "BE AFRAID" is
written in runes above it.
Sally opens the fireplace to meet the
creatures and finds one of the old housekeeper's teeth. The creatures
quickly prove to be hostile, stealing Alex's razor and shredding Kim's
clothes. Alex immediately blames Sally and finds a 19th-century silver
coin in her possession, which she found under her pillow after the
tooth disappeared. Alex and Kim head into town on a business trip and
Sally sneaks to the basement to talk with the creatures, but Harris
sends her away and tries to seal the fireplace. The creatures emerge
and brutally wound him with his own tools and he is hospitalized.
Sally's increasingly frightening encounters with the creatures prompt
Alex to call a therapist to talk to Sally, who draws a sketch of one
of the creatures that attacked her under her bedsheets.
Harris in the hospital, who tells her to find the unpublished artwork
of Lord Blackwood in the local library. The librarian reveals the
artwork, one of which is of a creature whom he describes as being like
tooth fairies, which every now and again turns a human into one of
their own. Kim races home as Sally is attacked again by the creatures
while having a bath, the lead creature being a transformed Lord
Blackwood who proclaims the creatures will make Sally one of their
own. Kim finds an undiscovered mural painted by Lord Blackwood in the
basement, depicting his son being transformed by the creatures. Kim
confronts Alex who is more interested in hosting a dinner for Mr.
Jacoby and friends. However, he finally realizes what is happening
when Sally is trapped in the library by the creatures, but she fends
them off by using her camera flash to distract them.
Alex and Kim
decide to flee the house with Sally, but both are ambushed by the
creatures and knocked out, Sally tries to wake Kim up but also gets
ambushed by the creatures and is knocked unconscious. When Sally wakes
up, her feet have been tied up with rope, and the creatures are
starting to drag her to the basement for her transformation. Kim
awakens and goes to basement confronting the creatures, cutting the
rope around Sally's feet but only to get herself in the ropes and her
leg broken by it as she struggles to get free. The creatures drag Kim
into the fireplace, as a distraught Sally crushes the creature who
used to be Lord Blackwood to death with a large flashlight. Alex
arrives just as Kim disappears, and the father and daughter mourn
Some time later, both return to the abandoned mansion to
leave a drawing of Kim there, but a gust of wind blows the drawing
into the creatures' lair, where the transformed Kim is heard
convincing the creatures to stay where they are and just go deeper
into the basement – for they will forget in time, and others will come
– claiming they have "all the time in the world".