I am a former Hair Stylist and some friends and family still ask me what shampoo and sometimes conditioner they should buy and can understand the confusion they feel with all the choices out there now.  Manufacturer's would like us to believe we need 20 different kinds of Shampoo and Conditioner for each member of the family.  Let's Address Baby's hair first:

I would buy a quality "Baby Shampoo" for baby for about the first year of life.  Don't use it on any other family member, it won't work well and is a waste of money then.  Most baby shampoos are low sudsing, easily rinsed out and not very effective cleansers. Using it just on baby would make a bottle last forever.  Remember, they are designed for babies with sparse thin hair that require very little cleansing.  But some can be harsh, so they can wreck chemically treated hair. 

Children's Hair:

Most shampoo manufacturer's have came out with children's shampoos and conditioners with fancy eye catching bottles and claim to be gentle.  They are for the most part "adult" products redesigned to be attractive to children.  They might have a different scent or label but are just the same as the adult version perhaps less conditioning.  Most children of course don't have chemically treated hair and these products seem to work well for them.  But if your child has long or curly hair they usually don't provide enough conditioning and comb-outs can be a nightmare.  If your child has long or curly hair step up to a much more conditioning shampoo and hair conditioner to de-snarl that hair and make both you and your child much happier.  A nice over-the counter product would be say Pantene or Dove (and use the conditioner too your child will thank you).  If your child have oily or especially dirty hair and it is not long you can use Pert or Prell.  Although quite harsh if used daily these shampoos are effective cleansers. 

Teenage Girls and Women:

Most Teenager's and Women and some Men now chemically treat their hair.  Color, Perms, Straighteners.  They need conditioning shampoos and a good hair conditioner to follow.  These can get expensive, rule of thumb save these products for only the people in the house who have chemically treated hair.  Use a good product I see no sense in spending enormous amounts of money to color, perm or straighten only to use some harsh stripping shampoo and fade your color, loosen your perm etc.  Matrix makes a good line of product Biolage comes to mind or Sleek Look or the line for colored hair.   If you don't choose a salon product at least use Pantene,  Dove, Herbal Essences Hello Hydration. 

Men or Women with Short Untreated Hair:

If your hair is short and you do not chemically alter it, you can use just about any shampoo or conditioner you choose.  If you have oily hair Pert, Prell are good cleansing shampoos.  Pantene is good for dry hair.  Even Suave products will work for you.  You won't need spend much to shampoo your hair.

Ethnic Hair:

Most people assume African Americans need to buy special or different Shampoo's and that Caucasians should never use them.  Wrong, hair is hair is hair.  As I stylist I seen all types of hair and ethnic hair.  You have to judge the hair by the individual not the race.  I have seen Caucasians with essentially "black" hair and African American's with Caucasian hair texture. 

Another myth is that African Americans should not wash their hair everyday.  Most African Americans do not wash their hair everyday due to the time and effort they have to put in to straighten and relax their hair.  They may be literally hours doing there hair.  If you wear your hair "natural" I do recommend washing it daily.  I won't strip the oils out or dry your hair if you are using a good product.  I recommend the Chi Line of products for all Ethnic/Curly/Frizzy hair that is treated, straightened, colored in any way.  Also try the Chi Silk Infusion, its wonderful stuff on any hair type.

I hope this helps!