Actually, many mail order brides in the past (back in frontier times) were brought in after a wife died. The male was to busy trying to keep the crops, going, animals fed and the farm kept up to take care of the kids. So a bride was advertised for, specifically to be a mom, take care of the house, kids, cooking cleaning etc.
And I find it hard to believe that a child should be the deciding factor in a marraige or relationship. I think you should consider their feelings, but to let them say yes or no about an adult relationship is absolutely ridiculous.

Of course a child would not want to share their mom or dad with anyone else. As an adult, you have to think about it and decide for yourself AND for the children. I mean, you're willing to let a person who would eat catain crunch and pizza for every meal decide wheter you should marry?
Pebbles and walle obviously have a connection that they feel is strong enough to build upon and make a life together. As for the wedding after the proposal.....most of the men I know don't jump into an engagement. they have to be prodded, poked, and in many cases given an ultimatum before "decide" to propose. Pebbles is just thinking ahead.
She's not the only one, there was a thread on the wedding boards (I think) about planning the wedding before the engagement. Many times, you know it's coming, so why not plan ahead. Buy some decorations you see on clearance. Again, in the past, women often prepared for their weddings as children. They needlepointed, quilted blankets, prepared a trousseau as children for their future marraiges. IMHO, it just makes everything easier...like a WDw trip, a wedding prepares planning. Why not start early?