Exodus 12:4

And if the household be too little for the lamb, let him and his neighbour next unto his house take it according to the number of the souls; every man according to his eating shall make your count for the lamb.

If the household be too little ... Since it was imperative that none of the paschal lamb should be left (Exodus 12:10), care was to be taken, by associating neighbouring families, that the party should be sufficiently large to ensure the entire consumption. Josephus states that, in later times, the normal rule required at least ten persons to constitute a proper paschal communion. But it is obvious, from the deflation given above of 'father's house, that it might comprise thirty or forty persons, for children of all ages were admissible as guests.

Moreover, while the lambs in Egypt were (and are) large, it must be borne in mind that "a male of the first year" would be an ample allowance on such an occasion, which was not a feast, but a religious solemnity, a very small portion-traditionally said to be about the size of an olive-being eaten by each individual.