What do I do with my 4 y.o. on the plane?

[Karenn]

The airline doesn't allow booster seats. Do I just use the lap belt with him?

[Joolsplus2]

Yup, just a lapbelt is fine (whole different set of crash forces at work, and generally you just want to be attached to the plane when you drop that 100 feet in turbulence). No boosters, because they require shoulderbelts.

Though, I saw a thing on MSNBC about a new harness coming out for kids 22-44 pounds.. not out yet, but looked cool!
Julie CPS Tech and mom to 3 in seats
http://www.cpsafety.com/articles/RFAlbum/SarahMA.aspx