Why does the Catholic church have so many Masses throughout the week? Why does the Catholic church have so many Masses throughout the week? For the practicing Catholic, which Mass service is most important? 

There are the weekly worship services, weekend worship services, and even holiday worship services. Where would Bible Study and devotionals fit in? Do children worship with the parents, or do they have their own little worship area/classroom setting where they learn about God and stuff?
Why does the Catholic church have so many Masses throughout the week?

It is because of what Mass is to the catholic church. Mass is the Single most important commandment given by Christ to do until the end of times (Do this in remembrance of me 
Lk 22 / 1 Cor 11).


  "At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic Sacrifice of his Body and Blood. He did this in order to perpetuate the sacrifice of the cross throughout the centuries until he should come again, and so to entrust to his beloved spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a paschal banquet in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us" (Sacrosanctum Concilium 47).


The mass is so important to the catholic church, that no-day passes without a Mass said at-least in one place in the world. This is not scientific, but it is folklore that there are three Masses being said every second in the world. (It is jokingly said that many Kings, dictators wanted to destroy the Catholic church. they tried different ways and failed. But all they have to do was to stop them from celebrating Mass.)

For the practicing Catholic, which Mass service is most important?

By the word important, if you mean the importance of the Mass itself, then for Catholics all mass is the same Calvary sacrifice, no one mass is greater than the other.

By the word important, if you mean the importance of participating in the Mass. Then important Mass would be Mass on Sundays and other Days of Obligation. There are specific ranks assigned to certain days. But this does not make the Mass more important (in the sense others are less important) in anyway. But it is important in the sense that they have to attend it.

Where would Bible Study and devotionals fit in?

First part of every Mass always starts with Readings from the bible. This is called the Liturgy of the Word. (Priests are required to read prayers from the bible three times a day. This is called divine office. Along with the Mass, divine office is the only public prayer of the Catholic Church)

On an ordinary day three passages are read. These passages are from:


Old testament or non gospel new testament. This is made into two separate passages on On Sundays and great feast-days (Solemnities)
Psalms (Some times, very rarely, other canticles from the bible too)
Gospel


After this during Liturgy of the Eucharist, all prayers said is based on biblical verses. So, in a way Mass is bible in action.

Do children worship with the parents, or do they have their own little worship area/classroom setting where they learn about God and stuff?

Mass is the primary form of worship in the Catholic church. There is a provision for a children mass where special prayers are said for them But worship is not to be done in a classroom setting. But almost as a norm Children always attend Mass with their parents. It is always recommended to do so. In-fact certain age children have a specific role in Mass called alter servers. Usually in parishes children (not toddlers) perform this role.

There is only one Mass for all. But there are separate Catechisms class (usually after Sunday mass) for Children.