Can other members of the household be questioned about their perception of the recipients' wellbeing before and after?
IMO it'd be ideal to ask them an open-ended "what changed about these people" to avoid priming effects.
However you choose to measure, be sure to check for any negative consequences of the donation. In adults, especially with mental health struggles, you may note resentment about how the aid was delivered or disappointment that it wasn't more.
It would be interesting to A/B test the impact of spending a lump sum like this, versus splitting the same sum over several weeks, months, quarters, or years. Part of experiencing a sense of security is knowing there'll be more where it came from -- so for instance it could be the case that giving a kid the interest from $1k as a monthly allowance might have greater positive overall impact than just giving them $1k worth of items all at once.