In each example, you're giving one instance in which the direct object ('the problem' or 'a meeting place') is the focus, and another instance in which the indirect object ('the children' or 'us'/'we') is the focus.
It is possible for passive structures to begin with either the direct object or the indirect object. Consider these examples:
- The gold medal was awarded to Sue.
- Sue was awarded the gold medal.
- The alphabet was taught to the students.
- The students were taught the alphabet.
In each case, both variations are equally strong - it simply depends on which noun you'd like to focus on within your context.
The problem is that some passive sentences sound awkward when lead with indirect objects - ones linked with verbs such as 'explain' and 'suggest'. "The children were explained the problem," and "We were suggested a meeting place," may be colloquially acceptable, but their meanings are not immediately understandable.
Unfortunately, there's not a clear distinction between which verbs are ill-suited for their indirect objects to take the focus of passive sentences, but here's a nice rule-of-thumb:
In an active sentence, if prepositions such as 'to' can be removed from before the indirect object, that indirect object can work well as the focus of a passive structure of that same sentence.
- The parents explained
to the children the problem. - removing 'to' doesn't work well.
- Richard suggested
to us a meeting place. - removing 'to' doesn't work well.
- The judges awarded
to Sue the gold medal. - it's an okay sentence without 'to'!
- The teacher taught
to the students the alphabet. - it's an okay sentence without 'to'!
Just as 'explained' and 'suggested' need 'to' or some similar preposition to come before their indirect objects, starting the passive forms with 'the children' and 'we'/'us' respectively creates awkward sentences. (Just remember that while we're focusing on the indirect objects here, it's the verb that determines how they can be used.)
All that said, it's always acceptable and correct to use the direct object at the start of a passive sentence. You can't go wrong with "The problem was explained to the children," or "A meeting place was suggested to us."