Can you please shed some light on the scriptural basis and applicability of two practices: the washing of feet; the presentation of babies before congregations?

I do not think the Bible teaches that the washing of feet was an ordinance intended for the practice of the church. When Messiah washed feet, it was in keeping with the traditional portion of the Jewish Passover, when the normal practice was to wash hands. However, Jesus took on the role of a servant and washed feet, telling the disciples that they should follow His example. The emphasis is not on the actual practice of foot-washing, but on the practice of choosing to serve rather than to rule. It is certainly not wrong for a church to practice it, but neither is it a biblical imperative.

Concerning dedicating babies, this is largely practiced by churches that do not practice infant baptism and, thus, use this as a substitute. Such churches are not violating any scriptural belief, and, so, there is nothing inherently wrong with this activity. However, again, it is not something commanded by Scripture.