There is no minimum age threshold where a child can be exempt from the requirements. Malagasy people are visa nationals and so each child must have an entry clearance in their own passport.
In the pre 9/11 era, children could travel with an amendment in their parent's passport, but it is no longer allowed. As a knock-on effect to requiring separate passports for dependents, the UK decided that every entry clearance needed to attract the same fee. And yes, there is a type of group application, but tour operators are required to have a qualification and it's basically irrelevant for you.
Applying as a Family
For your question about using the system... You would first complete the application for the primary (in most cases the father) and indicate in Part 9 that they are the primary. Write down their GWF number. Then proceed to make a fresh application for the other adults (presumably the mother). Put the primary's GWF number in Part 9 of each application and write down the other adult's GWF numbers. You should have all the adult's GWF numbers before starting the children's applications.
When you start with the children, write the names and GWF numbers for the parents in Part 7 of the application and make an additional note in Part 9. If they are relying upon your evidence for finance, make the appropriate note. There is no need to copy the same stuff over and over. This procedure is not taken from the rules, it is best practices only and reflects the way a qualified solicitor would do it. You can select a different procedure and get a comparable effect.
Children under 18
For your question about finding things on the net, you can read the guidance and note that there is separate guidance for children under 18. Those two things are all you really need. Beyond that, there are not many up-to-date narratives or FAQ's on the net and trying to use them is not always beneficial.
Practical advice: try to fill out the applications in one session when everyone in your country is asleep. That way you have a better chance of getting their biometric appointments at the same time. If the system splits up the appointments, send the whole family to the first appointment anyway.
- All applicants attract the same fee (regardless of age).
- Applicants should include marriage certificates and birth
- If you already have a valid UK visa, you can (and should) be the
primary. In this case use your entry clearance number instead of GWF number.
- Children need their own login and password.
- Multiple email addresses may be required.
- If different appointments get scheduled for family members, they
should all show up at the primary's appointment and be processed
together. As a matter of policy, families should not be separated at any stage of the process.
- The primary submits one set of evidence. Payments should be separate.
- Practical advice part 2: take extra care in your cover letter to
assure that you will be in the arrivals area to meet the children and
you will arrange for their safe transportation to your residence.
- It is fundamentally critical that the application contains child