People take pedigree dogs seriously, and pedigree cattle, but with chickens there is no one to watch over things and ensure that breeds are not crossed with each other. Most likely, you have chicks that are mostly Mottled Houdan, but contain a little of something else. The person or hatchery who bred these chicks may not even know they aren't pure bred.
You will be able to tell a bit more about what is going on when the birds are full grown. If there are a lot of other things going on, like if they have big wattles/no beard, or if they have a single comb, that would offer clues as to their ancestry.
Good luck and enjoy.
Houdans will generally be
* unusually friendly as young adult chickens. Young friendly roosters may turn angry when mature
* active chicks, feather out fast, love to fly
* white egg layers
* rarely broody, not a committed mother
* hens have a round crest shaped somewhat like a dandelion seed head. They may have a fairly small crest
* roosters have a spreading crest (like a half open dandelion flower) that goes mostly backward (like they are facing into a breeze).
* Houdans have a double comb, which might be like a "V" or it might be like two little bunches of coral or the tips of a pair of antlers. On hens, it may be two bumps that you can only see if you push back the feathers
* Houdans have a white skin which is thin, almost translucent
* Houdans have thin, light bones (ie narrow toes, and thin shanks)
* Houdans often have a fairly upright, perky tail
Be suspicious if your Houdan
* has a body shape unlike a Houdan
* has a wide, flat, parasol-shaped crest like a white crested black polish
* has a very long, low tail like a white crested black polish
* has no comb at all (like many white crested black polish)
* has 4 toes on both feet
* has no beard, has large dangling wattles
* is very very skittish and terrified when held
* is very broody
* lays brown eggs
* has yellow skin
* has thick, rubbery skin
* has red earlobes
* has very heavy brows like an Orloff
If you're going to breed Houdans for fun, try to avoid breeding from any that are "suspicious"