As I already said, If the primary applicant's already in Belgium, the dependent visa process in very complicated. Along with the re-issue of documents and Legalization, one worry will add-up - that's the quality residence at Belgium. Below are list of documents needed.

1. Belgium Residence ID of the primary applicant
2. Proof House - Sufficient space for the family to live
3. Medical Insurance for your spouse/family
4. Bank Statement - 6 months
5. Salary Slip - 6 months
6. Employee Attestation
7. Request letter for legalisation
8. Marriage Certificate - to be legalized
9. Birth Certificate - to be legalized
10. Color Photos of the primary applicant

You have to move in to a bigger house in Belgium, based on the number of dependents. Their local officials come and check your apartment before they give clearance for the house (Sl#2). It's not only the space, they also check for all the safety (electrical, fire, security, open area....and many). If you’re in Belgium to earn some money, your plans will be gone!. If you want your wife and Kid with you, be ready to spend 1500+ Euros for apartment rental.

My advice is always process your dependent visas along with the primary applicant visa. Never do the mistake thinking that you’ll call your dependents later, which may end-up like you’ll never get your dependents :P