You indicate that your support is enforced through “MEP”, which we understand to be the Alberta Maintenance Enforcement Program (which is the approximate equivalent to Ontario’s Family Responsibility Office, or “FRO”). Both of those provincial government organizations are responsible for collecting court-ordered child support, and distributing it to the recipient parent.
The precise scope and details of your obligation to pay child support are documented in your particular court order that has been registered with MEP. That order has been customized to your situation, and will set out the specifics around whether you do (or do not) have a duty to supply your children with separate clothing and jackets on top of paying child support.
If such an obligation does not appear in the terms of the order governing your and your Ex’s situation, then – without knowing more of your details – it is very unlikely that you can have it unilaterally imposed on you now. However, you should seek the advice of a local Family Lawyer who will look at the terms of your order, and can confirm the precise extent of your financial obligations in this regard.