One of our parish priests invites the children present to join him and to stand around the altar during the consecration. Is this practice acceptable?
While the intentions of the priest are most likely good, the action of inviting anyone around the altar during the Eucharistic Prayer (other than clergy) is illicit.
The Congregation for Divine Worship addressed this in 1981, Notitiae 17 (1981) 61:
Question: At the offertory of a community Mass, some (religious men and women, lay persons) bring down the bread and wine to be consecrated to the altar, and these gifts are accepted by the celebrating priest. All the participants together accompany the procession in which the gifts are brought forward, and they stand around the altar until communion. Is this manner of acting in conformity with the letter and the spirit of the Roman Missal?
Answer: Certainly the Eucharistic celebration is an act of the community, which is carried out by all the members of the liturgical assembly. Yet each person ought to have and keep his own place and the role proper to himself: « each minister or member of the faithful, performing his own role, should exercise solely and completely what pertains to him according the nature of the matter and the liturgical norms » (« Sacrosanctum Concilium », n. 28).
In carrying out the eucharistic liturgy, only the celebrant who is presiding remains at the altar; the assembly of those participating hold their place in the church outside of the sanctuary, which is reserved for the celebrant or concelebrants and the ministers.