When you are working as freelancer (zzp-er) or self-employed with employees in the Netherlands it is not, mandatory to have insurance for illness, invalidity or unemployment. You have to make arrangements for social insurances yourself if you want to receive any benefit if you become ill or unable to work. However. Maternity leave and childcare is however possible when you are not insured. Check UWV for more information.
National insurance schemes (social security) are compulsory for everyone working or living in the Netherlands. Freelancers/self-employed professionals in the Netherlands pay national insurance contributions through their income tax.
Everyone living or working in the Netherlands is legally obliged to take out standard healthcare insurance. Thus this also applies to the self-employed. You can choose if and which additional insurance you wish to take out.
Other insurances are voluntary. You should consider the risks you are willing to take. If you do not have insurance you may have no income if, for instance, you fall ill, you have to terminate your business, or during the period around childbirth.
Do you want to receive an income if you fall ill or in case of occupational disability? You need to arrange for this yourself. You can set aside money for such instances or you can take out insurance: